I have a 1992 f150 5.0 auto. when the truck is warmed up the torque convertor engages when it shifts in to 3rd gear, at the same time. causing a major drop in rpm. it shifts normal when it is not warmed up. 1,2,3, then overdrive then the torque convetor locks up droping the rpm down in a normal range. i have no slipping or shuttering.

Fuse # 20 or 21 gets power through ignition. This fuse controls PRNDL indicator, speedometer, tach, & will cause transmission to not shift gears correctly. Ours took off in 3rd gear when put in Overdrive & only ran in 3rd gear. If we tried to manually shift thru gears (auto trans), it had 1st, 3rd, reverse. No 2nd or over drive. Replaced ignition. Fixed problem. Root problem was Electric motor that engaged 4 wheel low side was bad. Every time we used 4 Low side it threw power surge through ignition & blew ignition out. Good Luck.

actually it is called a lock out torque convertor. when you go into 3rd gear and reach certain conditions it will lock the torque converter making it like a standard shift. so basically it is a 4th gear. this is done for fuel economy.

Check your ignition coils. One of mine was bad and when I replaced it, the shifting issue stopped.

This is a situation of low pressure,as you warm up the vehicle the transmission fluid is warmer which allow the torque convertor to produce pressure to collapse the clutch pack and transfer power for a shift gear,your solution is a torque convertor and a front pump

there is a total of 27 diagnostic steps to follow, but here is some info for you:
SYMPTOM
P1740-TCC O/D SOL PERFORMANCE

WHEN MONITORED
The Torque Convertor Clutch (TCC) and Overdrive Clutch (O/D) will be tested each time the PCM requests TCC engagement in 3rd gear and O/D.

SET CONDITION
The code will set if the expected RPM drop is not achieved while attempting to engage TCC or O/D. This indicates a malfunctioning torque convertor or overdrive clutch.

POSSIBLE CAUSES
- Camshaft DTC present
- Engine RPM DTC present
- Fuel level low
- Misfire DTC present
- Output speed DTC present
- P1765 DTC present
- Park/Neutral DTC present
- PTO engaged (if equipped)
- Torque converter clutch DTC present
- TPS DTC present
- Transfer case in low range (if equipped)
- Transmission Relay DTC present
- Transmission temperature too cold
- Intermittent
- Check transmission fluid-debris
- Check transmission fluid-stall
- 3-4 Shift Solenoid
- Oil Pan contains excessive debris
- Shaft or seal damage
- TCC solenoid
- Torque converter
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this is a known issue with the gm 4L60E transmission. the valve body in transmission causes this. if it is wore, then less fluid is sent to shift selonoids. thus causing torque convertor not to lock up, and this causes slipping. if it slips 2 consecutive trips then the transmission detects this and should turn on check engine light. ( p1870 ). you can see if the tcc solinoid is bad. but if not its usually the valve body in tranny.

SYMPTOM
P1740-TCC O/D SOL PERFORMANCE

WHEN MONITORED
The Torque Convertor Clutch (TCC) and Overdrive Clutch (O/D) will be tested each time the PCM requests TCC engagement in 3rd gear and O/D.

SET CONDITION
The code will set if the expected RPM drop is not achieved while attempting to engage TCC or O/D. This indicates a malfunctioning torque convertor or overdrive clutch.

POSSIBLE CAUSES


Camshaft DTC Present
Engine RPM DTC present
Fuel level low
Misfire DTC present
Output speed DTC present
P1765 DTC present
Park/neutral DTC present
PTO engaged (if equipped)
Torque converter clutch DTC present
TPS DTC present
Transfer case in low range (if equipped)
Transmission relay DTC present
Transmission temperature too cold
Intermittent
Check transmission fluid-debris
Check transmission fluid-stall
3-4 shift solenoid
Oil pan contains excessive debris
Shaft or seal damage
TCC solenoid
Torque converter

if it has overdrive transmission the torque convertor has a vein broke inside causing shudder replace torque convertor.
the torque conver does the overdrive when it hits a certain rpm it upshifts to overdrive in torque convertor.
with vein broke it hrows it out of balance causing it to shudder and possibly slip.

Check your auto transmission levels. Slow, often jerky, gear shifting is often accompanied by a bit of a jolt when putting it into drive from park or neutral. When fluids are low the torque converter impeller has to work harder to get pressure up and therefore it is slower at shifting to the next gear . Low transmission fluids also lead to poor fuel consumption.

Her is the definition and a list of possiable causes.


Code P1740-Torque converter clutch did not lock up when the PCM sent the command. Enabling conditions: No engine or transmissions codes are present, vehicle speed was under 70 MPH, TPS was under 33% open. When the PCM commanded the torque converter to lock, no change was detected in engine speed. Blocking action: This code can block the following monitors: none.
Testing: Check torque converter solenoid for proper operation.
P1740 TCC O/D SOL PERFORMANCE (GAS)
Theory of Operation
The Torque Converter Clutch (TCC) Solenoid is used to engage the TCC which improves fuel economy.
When Monitored
The Torque Convertor Clutch (TCC) and Overdrive Clutch (OD) will be tested each time the PCM requests TCC engagement in 3rd gear and OD.
Set Condition
The DTC will set if the expected RPM drop is not achieved while attempting to engage TCC or OD. This indicates a malfunctioning torque convertor or overdrive clutch.
Possible Causes
* ENGINE DTCS PRESENT
* TRANSMISSION DTCS PRESENT
* TRANSMISSION TEMPERATURE TOO COLD
* OIL PAN CONTAINS EXCESSIVE DEBRIS
* 3-4 SHIFT SOLENOID
* SHAFT OR SEAL DAMAGE
* TCC SOLENOID
* TORQUE CONVERTER