Shift solenoid relay.. internal or external?

What are you talking about auto shift control solenoid ? Which transmission does yours have ?
Automatic Transaxle - 3T40 Automatic Transaxle - 4T40-E
1-2 Shift Solenoid Valve
In transmission valve body
Transmission Component Location
Automatic Transmission Internal Connector End Views
2-3 Shift Solenoid Valve
In transmission valve body
Is there a DTC - diagnostic trouble code stored ? Which gear or gears are not working ?

1st.. check fuse for clutch solenoid/relay. 2nd... replace clutch solenoid/relay. 3rd... check for damaged wiring to trransmission or connector to transmission. If all these are correct, see your Ford Dealer.

TCC locks at high speeds. where is yours failing, how fast.?

so at what speed, do you expect TCC lockup.?
unless you have tranny slip.. a whole other problem in any gear.

this old tranny has, pure mechanical ops. no TCM here.
most old tranny have the foolwing inputs.
1: driver right foot called the TV cable or detent or passing gear cable.
it can stick and cause late shifting
2: Tail shaft speed, this is the tail speed governor that shifts by speed.
3: the load vacuum modulator that shifts by engine load (vacuum)
4:gear lever positions PRNDL.

the 5th input is the TCC relay that the ECU controls
the ECU activates it under inputs of RPM and MPH (VSS1)
so if the relay closes at the right speed, then the ECU and relay
are working, if the TCC lock up is delayed, then the TCC internal
solenoid is bad, leaks or the acutal lockup is bad or pump pressure
is too low, or any leaks from the solenoid to the locker slave.

code p0730 refers to incorrect gear ratio.==causes --wiring--TR sensors/switch--shift solenoids--transmission mechanical fault
code p0780 refers to gear selection--shift malfunction====causes--wiring--TR sensor---shift solenoids--transmission mechanical fault.. have the shift solenoid checked out. Have a pressure test done on the transmission to check for internal damage.

P0700 is a informative transmission code, about some problem there; the P0733 and P0734 is the specific problem there.
I would first try changing the fluid and filter. Although the fluid may look like it is brand new, with 100K on the fluid, I can assure you that even if those miles were all highway at steady speed and no load that the fluid has deteriorated and no longer lubricating the internal parts properly and that there is some debris in the ******.If codes return and shifting problems are still present, there is definite internal failure, possibly the pump or in the clutches.
DTC P0733The powertrain control module (PCM) uses the crankshaft position (CKP) sensor, input speed sensor (ISS) and output speed sensor (OSS) to determine engine speed, input shaft speed and output shaft speed. These sensor readings are used to determine the current gear ratio and RPM slip across the torque converter. The PCM uses this information from the sensors to determine if the commanded gear matches the actual gear. During normal driving conditions, the PCM will adapt main line pressure via the pressure control (PC) solenoid to prevent slipping and harsh shifts. Shift solenoid 3 is used to apply or release third gear clutch. The PCM controls 3rd gear by controlling the ground for shift solenoid 3. The PCM will turn the solenoid OFF, open the driver circuit, when 3rd gear is commanded On to apply 3rd clutch. Shift solenoid 3 is supplied ignition voltage from the fuel pump relay whenever the PCM commands the fuel pump relay ON. DTC P0733 sets when 3rd clutch still slips after the PCM has commanded high main line pressure.DTC Parameters
DTC P0733 will set if the PCM detects an incorrect actual 3rd gear ratio when 3rd gear is commanded On when:- The condition exists for longer than 3 seconds (2001)*- The condition exists for longer than 3 seconds, 1 minute is allowed to elapse, then condition exists again for longer than 3 seconds (2000)- The high main line pressure has been commanded- The transaxle is in a forward gear- The input speed is greater than 224 RPM- The vehicle speed is greater than 5 km/h (3 mph)- The speed noise parameter = NO- The steady state ratio fail counter equals 255 for an in-gear failure, or the shift fail counter is greater than 100 on a downshift or upshift to 3rd gear (128=0 or normal operation)DTC P0733 diagnostic runs continuously once the above conditions have been met.
DTC P0733 is a type A DTC for 2000, type B for 2001.**Applicable to vehicles built after June 2000.
Diagnostic AidsImportant: If DTCs P0745, P0746, P0756, P0758, P0761, P0763, P0766, P0768 or P0789 is set, diagnose that DTC first. A diagnosed PC solenoid, shift solenoid 2, 3 or 4 low/high circuit fault DTC may have caused DTC P0733 to set.Important: If a shift solenoid performance DTC P0783, 4th gear stuck ON, is set, diagnose that DTC first. A 4th gear stuck ON may cause no 3rd gear, no 2nd gear, or TCC stuck Off.
Refer to Pressure Ports - Air Check and Parts Description for pressure apply points and for component/location description.
Possible causes of no 3rd gear are listed in the flowchart on the succeeding page.
Verify TRANSMISSION ISS and TRANSMISSION OSS read correctly on Scan tool.
Make sure the pressure control, shift 2, shift 3 and shift 4 solenoids are not intermittently sticking. A sticking shift solenoid 4 may cause 4th gear to be applied from an initial start resulting in no 3rd gear. Audible sound should be similar for all solenoids. A muffled tone indicates the need for replacement.
Check this pinout HERE
P0734 refer at ratio 4 gear, and the rocedure is the same.
Hope helps.

P0763 - Shift Solenoid C Electrical
Possible causes- Faulty shift solenoid C valve
- Shift solenoid C valve harness or connectors
- Shift solenoid C valve circuit is open or shorted
- Low transmission fluid level
- Dirty transmission fluid
When is the code detected?The P0763 code is detected when the gear required by the ECM does not match the actual gear when vehicle is driven.Symptoms- Engine Light ON (or Service Engine Soon Warning Light)
- Transmission will not shift gears.P0763 Description Shift solenoid valve C is turned ON or OFF by the Transmission Control Module (TCM) in response to signals sent from the park/neutral position (PNP) switch, vehicle speed and Engine Control Module (ECM) (throttle opening). Gears will then be shifted to the optimum position.

P1600 - Loss of KAM (Keep Alive ECM memory) Power; Open Circuit

Check all fuses related to the ECM

P0700 is a informative transmission code, about some problem there; the P0733 and P0734 is the specific problem there.
I would first try changing the fluid and filter. Although the fluid may look like it is brand new, with 100K on the fluid, I can assure you that even if those miles were all highway at steady speed and no load that the fluid has deteriorated and no longer lubricating the internal parts properly and that there is some debris in the ******.If codes return and shifting problems are still present, there is definite internal failure, possibly the pump or in the clutches.
DTC P0733The powertrain control module (PCM) uses the crankshaft position (CKP) sensor, input speed sensor (ISS) and output speed sensor (OSS) to determine engine speed, input shaft speed and output shaft speed. These sensor readings are used to determine the current gear ratio and RPM slip across the torque converter. The PCM uses this information from the sensors to determine if the commanded gear matches the actual gear. During normal driving conditions, the PCM will adapt main line pressure via the pressure control (PC) solenoid to prevent slipping and harsh shifts. Shift solenoid 3 is used to apply or release third gear clutch. The PCM controls 3rd gear by controlling the ground for shift solenoid 3. The PCM will turn the solenoid OFF, open the driver circuit, when 3rd gear is commanded On to apply 3rd clutch. Shift solenoid 3 is supplied ignition voltage from the fuel pump relay whenever the PCM commands the fuel pump relay ON. DTC P0733 sets when 3rd clutch still slips after the PCM has commanded high main line pressure.DTC Parameters
DTC P0733 will set if the PCM detects an incorrect actual 3rd gear ratio when 3rd gear is commanded On when:- The condition exists for longer than 3 seconds (2001)*- The condition exists for longer than 3 seconds, 1 minute is allowed to elapse, then condition exists again for longer than 3 seconds (2000)- The high main line pressure has been commanded- The transaxle is in a forward gear- The input speed is greater than 224 RPM- The vehicle speed is greater than 5 km/h (3 mph)- The speed noise parameter = NO- The steady state ratio fail counter equals 255 for an in-gear failure, or the shift fail counter is greater than 100 on a downshift or upshift to 3rd gear (128=0 or normal operation)DTC P0733 diagnostic runs continuously once the above conditions have been met.
DTC P0733 is a type A DTC for 2000, type B for 2001.**Applicable to vehicles built after June 2000.
Diagnostic AidsImportant: If DTCs P0745, P0746, P0756, P0758, P0761, P0763, P0766, P0768 or P0789 is set, diagnose that DTC first. A diagnosed PC solenoid, shift solenoid 2, 3 or 4 low/high circuit fault DTC may have caused DTC P0733 to set.Important: If a shift solenoid performance DTC P0783, 4th gear stuck ON, is set, diagnose that DTC first. A 4th gear stuck ON may cause no 3rd gear, no 2nd gear, or TCC stuck Off.
Refer to Pressure Ports - Air Check and Parts Description for pressure apply points and for component/location description.
Possible causes of no 3rd gear are listed in the flowchart on the succeeding page.
Verify TRANSMISSION ISS and TRANSMISSION OSS read correctly on Scan tool.
Make sure the pressure control, shift 2, shift 3 and shift 4 solenoids are not intermittently sticking. A sticking shift solenoid 4 may cause 4th gear to be applied from an initial start resulting in no 3rd gear. Audible sound should be similar for all solenoids. A muffled tone indicates the need for replacement.
Check this pinout HERE
P0734 refer at ratio 4 gear, and the rocedure is the same.
Hope helps.

It means shift solenoid B inductive signature. Basically, the van is not able to properly control it's shifts due to either an electrical problem leading in to the transmission solenoids or due to an internal transmission issue. This is not something you really want to mess around with. The transmission sounds like it is basically in 'fail-safe' mode meaning that it is trying to protect itself even though there is a problem in the system. I highly recommend you get it to a shop ASAP so that you minimize the damage.

You need to find someone who can pull the codes from the transmission and see what kind of trans fault it is. If there is a fault in the trans the controller will put it into limp in mode which is 2nd gear locked. Won't shift out of 2nd...You need to pull the codes and see if it is internal in the trans or an external sensor-Good Luck

two issues here. this may be a low fluid issue. i would check the level of the fluid first. the next issue could be a blown shift solenoid. these are located inside of the transmission pan.also, check the filter as well.(transmission filter could be clogged)