Can the restricted torque converter be altered to work as it should?

Lockup converter, overdrive, torque converter lockup solenoid, spark plugs and restricted injectors .

torque converter clutch stuck or not working properly

Common Problems That Trigger the P0740 Code
Defective Torque Converter Lockup Solenoid
Defective Engine Coolant Temperature Sensor
Defective Torque Converter Clutch
Defective Valve Body
Dirty transmission fluid that restricts the hydraulic passages

Check you transmission fluid. It sounds like a Torque Converter Lockup Solenoid problem though.

Also there was a Tech Support Bulletin related to the Torque Converter listed. Make sure you have taken your vehicle in to get it taken care of.

CUSTOMER SATISFACTION NOTIFICATION NO. C01 3/8" TORQUE CONVERTER DRAIN BACK VALVE
Issue Date: 01/2003

NHTSA Campaign ID number:
Potential number of units affected: 30,000
Model year(s): 2003
Manufactured: 10/15/2002 - 11/18/2002
Owner notification start date: January, 2003 Defect: 2003 models equipped with a 4.0L engine only.
Consequence: The torque converter drain back valve on affected vehicles may contain a check ball that swells. A swollen check ball will restrict fluid flow to the cooler and cause the transmission to overheat. This could cause transmission damage.
Solution: The torque converter drain back valve assembly must be replaced.

CODE PO1870 IS TRANSAXLE COMPONENT SLIPPING CONDITIONS.LOOKING AT POSSIBLE CAUSES TRANSMISSION VALVE BODY NEEDS OVERHAUL ALL SHIFT VALVES HAS SEDIMENT DAMAGE OR LEAKING SEALS.THE TORQUE CONVERTER FRONT STATOR SHAFT BUSHING IS WORN THE STATOR ROLLER CLUTCH IS NOT HOLDING.THE TORQUE CONVERTER CLUTCH VALVE STUCK.PUMP TO CASE GASKET LEAKING.THE ORIFICE CUP PLUGS ARE RESTRICTED OR DAMAGED.

VSS Sensor The Vehicle Speed (VSS) Sensor input is used by the PCM to determine vehicle speed. The VSS generates a signal that increases in frequency proportionate to vehicle speed. The PCM has a base frequency stored in memory for a distance of one mile. By comparing the input and stored value, the PCM calculates vehicle speed.
VSS types include: photo-optic, permanent magnet generators or hall effect technology. The PCM may use other sensors on the vehicle (ABS Wheel Speed) to validate VSS operation.
VSS information is used to calculate vehicle loads including: torque converter application, cruise control, fuel cutoff/speed governance strategies, instrument panel speedometer and more.
Modified drivetrain components such as final gear sets and/or tires can alter VSS input values to the PCM. Improper signals can alter Torque Converter Clutch (TCC) application, shift points, cruise control operation as well as many other systems relying on vehicle speed input.
Typical VSS

WARNING
To avoid personal injury and/or vehicle damage, refer to the service precautions at the beginning of this section.

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The Speedometer may not work due to a break in the wire for the VSS, or a bad VSS or a bad instrument cluster.

TORQUE CONVERTER IS STUCK THIS IS THE POSSIBLE CAUSES LIKE INTERNAL DAMAGE.OIL PRESSURE TOO LOW.CONVERTER CLUTCH VALVE STUCK.RESTRICTION IN OILN PASSAGES.LEAKS OR CRACKS IN THE FILTER.FAULTY CONVERTER CLUTCH SOLENOID.WHICH WILL CAUSE CONVERTER NOT TO RELEASE.

TORQUE CONVERTER CLUTCH SYSTEM STUCK ON.PROBLEM COULD BE PRESSURE REGULATOR VALVE IS STUCK.OR THE TCC FLUID CIRCUITS LEAKING OR ABNORMALLY LOW HIGH LINE PRESSURE.OR THE TCC RELEASE SWITCH CIRCUIT IS SHORTED TO GROUND.CHECK TRANSMISSION FLUID LEVEL.IF TRANSMISSION FLUID LOOKS REAL DARK LOOKING AND SMELLY .CHANGE THE FLUID AND FILTER.IF THIS DONT HELP ! YOUR PROBLEM COULD BE A BAD TORQUE CONVERTER CLUTCH SOLENOID OR INTERNAL DAMAGE INSIDE TORQUE CONVERTER.OR RESTRICTION IN OIL PASSAGES AND STOPPED UP OR BLOCKED TCC SCREEN.

it could many things.it could be torque converter internal damage -converter solenoid grounded or converter clutch valve stuck- oil pressure too low-restriction in oil passage.scan it.to check see if TCC SOLENOID.FIRST BEFORE REMOVING TRANNY TO REPLACE OTHER PARTS.

sound like torque converter problems.scan it to check torque converter.make sure it is applying and releasing .if not you got a bad torque converter solenoid.or a stop up screen.restriction in oil passages .or the o-ring seal cut or damage.also check for low oil pressure.