Having a drivability problem (98.5/24V/4sd auto/4x4/4.10 gear) I’m losing about 200 rpms at speed. Feels like its losing torque converter lock up at about 70 mph. Lock up is obvious and strong at 45 mph but at 70 the rpms will fluctuate between 2100 and 2400 with no change in speed. Changed out the tcc solenoid/over drive solenoid, governor solenoid and governor pressure sensor no change. Installed manual tcc switch, sitting still, truck in drive flipped the switch and killed the engine but no change in lock up at speed. Some lose in fuel economy, about 1mpg. Took it to a transmission shop they said they couldn’t find anything wrong, computer commands lock up at the right time and there’s no codes. Performance is down at speed also, rpms come up then speed increases, not together. Normal rpm/speed is 1900=60, 2150=70, 2400=75 with no fluctuation. Serviced the transmission with the electronics install, the pan and fluid were extra clean no sign of damage or wear. Battery terminals are clean and body grounds have been scraped. I’m not sure where to look next. Thanks :banghead:

Have you tried to calibrate the APPS? if not do that first and see if it helps.

Another one I thought of that could be a issue is the brake light switch. This controls locking/unlocking of the TC. I've heard where a lazy pedal could be just enough weight to trip (flicker the brake lights) and cause this lock.unlock weirdness.

I saw a voltage fluctuation from the APPS sensor of .4 volt. Could that indicate a problem? I will try to calibrate tonight.

---------- Post added at 11:19 AM ---------- Previous post was at 11:18 AM ----------

I put my left foot under the break pedal and lifted up on the pedal and saw no change. Is there another way to rule this out?

I saw a voltage fluctuation from the APPS sensor of .4 volt. Could that indicate a problem? I will try to calibrate tonight. I put my left foot under the break pedal and lifted up on the pedal and saw no change. Is there another way to rule this out?

Hmmm... Just replace the brake light switch since there is no way I know of to adjust the switch... Now is the APPS sensor still showing this .4 volt change all the time or only randomly?

The .4 fluctuation was with cruise set driving on a level road and it was spiking up to .4. What is the propper proceedure to calibrate the APPS sensor? I did the APPS learn proceedure.

Ok... Now does it do this without the cruise set? Funny feeling the PCM is at fault... (Cruise control)

I did the apps relearn (key on pedal down and back up slowly) and the truck has been back to normal for the past two days. It can't be that esay?