1993 gmc k1500 pickup. speedometer reads way above actual vehicle speed and when it is all the way to 80mph and i put on a turn signal or anything else electrical the speedo jumps up and down without vehicle speed changing. already replaced transmission speed sensor so thats not it? HELP!!!

What sensor did you change . VSS - vehicle speed sensor or output speed sensor .
The ideal what to find the problem would be to hook up a factory scan tool to see the VSS is put out a signal to the PCM/ECM , then see if the PCM /ECM is sending info to the instrument cluster ,. And knowing how these this work couldn't hurt either .

The IPC displays the vehicle speed based on the information from the PCM. The PCM converts the data from the vehicle speed sensor to a 4000 pulses/mile signal. The IPC uses the vehicle speed signal circuit from the PCM in order to calculate the vehicle speed. The speedometer defaults to 0 km/h (0 mph) if a malfunction in the vehicle speed signal circuit exists.

Have the vehicle checked for DTC"S - diagnostic trouble codes . No all code's turn on the check engine light .
DTC P0608
The PCM creates the vehicle speed output signal by pulsing the circuit to ground. The PCM pulses the circuit at the same rate as the vehicle speed signal input. The PCM monitors the voltage on the vehicle speed signal circuit. If the PCM determines the voltage is out of the normal operating range, a DTC sets.

Install a scan tool.
Raise the vehicle's drive wheels. Refer to Lifting and Jacking the Vehicle in General Information.
Start the engine.
Place the transmission into drive for an automatic transmission or third gear for a manual transmission.
With the scan tool, observe the Vehicle Speed Sensor parameter in the PCM data list.
Does the Vehicle Speed Sensor parameter match the speedometer display?

This is something best taken to a qualified repair shop . This could be a wiring issue , or the PCM or the instrument cluster .

You may need another speedometer. The speed sensor sends a signal to both the speedo and the odometer. So if the sensor fails, both meters would stop working.
The speedo gets power from the same circuit as the warning lights.

Hello
This problem is caused by a defective instrument cluster and it must be send out for updated parts and repair of defects in the design. Although the instrument cluster in this truck uses what looks like analog instruments it is actually digitally controlled by a small computer inside the cluster assembly, this same computer it seems sends the signal to the cruise control as well, so if the speedometer needle is getting a faulty signal then the cruise will act up as well. There are many places on the Internet that can do this repair, you are not stuck with the dealer who will 2X the cost of the repair of the cluster to you (capitalization in all it glory). These companies will send a special box to ship the cluster in and provide full instructions on removal.
Below is one such link to a cluster repair service, give them a call about your particular problem.

http://www.instrumentclusters.com/

It can be faulty vehicle speed sensor .The sensor connects to the differential.The sensor in the transmission that tells the instrument panel how fast the transmission is turning. Sometimes that sensor breaks.
There is a speed sensor on the transmission that sends a signal to the
speedometer control on the back of the instrument cluster, and diagnosis is
pretty straightforward. The On-board Diagnostics Generation II (OBD II)
scan tools used by professional technicians should have the ability to read
the signal generated by the transmission speed sensor and therefore check
the function of the speed sensor. Even if the technician's scan tool does
not have this capability, the sensor can be checked with a volt meter at the
sensor itself.

If the sensor is putting out the proper signal, then the next step would be
to check the wiring between the speed sensor and the speedometer control by
checking the signal at the wire harness at the speedometer control. If the
signal is good, then the speedometer control is bad, and if the signal is
bad, then the wiring between the sensor and speedometer control is bad. The
most time confusing part of doing all these checks would be removing the
instrument cluster to get at the speedometer control, about a half-hour
total for all the checks.---------- If the needle moves you have a broken pinion or counter gear.If not, then I would replace both speedometer cables.---------------Thank you.

They don't have cables, the speed signal is delivered electronically to the computer then to the instrument cluster. If your gauges aren't reading correctly it's most likely due to failing stepper motors on your cluster's circuit board, very common on all 03-06 GM vehicles. Check out this page to read more about it and see how to get it fixed - Sierra speedometer repair

the speed sensor on the GM vehicle works for two things
the speedometer and the overdrive only

its your u joints i had the same problem!!!

The 5 speed trans. has a back up light switch on the left side of the tranny (as you face front of truck), check to see if it's shot ($10 part, screws in)

i Have 96 Taurus, may help you. May be a little different on 93. good luck. please rate if this is what you need.
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3.0L (2V) and 3.0L (4V) Engine
The vehicle speed sensor (VSS) (9E731) is:

• a Hall-effect pickup that sends a signal to the powertrain control module (PCM) (12A650).
• able to provide the VSS signal which tells the powertrain control module vehicle speed.

Vehicle Speed Sensor (VSS) (Except SHO) Removal and Installation

1. Disconnect battery ground cable (14301) and positive battery cable.
   

1. Raise and suitably support vehicle on hoist. Refer to Section 00-02 .
   

1. Remove three bolts, seven nuts and Y-pipe assembly from vehicle.
   

1. Disconnect vehicle speed sensor electrical connector.
   

1. Remove vehicle speed sensor retaining bolt and vehicle speed sensor (VSS) (9E731) from transaxle.
   

1. To install, reverse Removal procedure. Tighten VSS retaining bolt to 3.4-4.5 Nm (31-39 lb-in). Tighten Y-pipe assembly nuts and bolts to 34-46 Nm (26-34 lb-ft).
   

this may be due to a poor connection at the vehicle speed sensor on the transmission, pull the connector off the sensor and clean it with contact cleaner, if the problem persists replace the speed sensor. there are 2 diff ones here is a picture of the most common one for an auto trans.