Hey guys. I was driving on alot of mountain roads today driving to and from Catskill State Park from Cobleskill and I noticed something weird with the RPMs and I don't know if it is my tranny or not. If I accelerate from a stop or very slow speed to just after 2nd gear and then slowly let up on the gas pedal (if it seems to be approaching a shift point) to slow down, the RPM seems to fluctuate up then down a bit (from 2500 RPM and it fluctuates + or - 100-200 rpm) and then drop when it shifts again. This is especially true on hills if I back off on the throttle (I always use 3 on hills). It seems to do the same thing with 3rd gear (when I let it get to 3). It seems to do it whether the shift lever is in 3 or D. The fluid color hasn't changed since I had it changed in January and it is still a nice pink color and it has just a little over 5,000-6,000 on the fluid. The truck has a B&M tranny cooler (see my album) and I also had the shop put Lucas Trans Fix in it for preventive maintenance when they flushed the fluid (fluid ONLY. The filter was done last year at 72,000 when they did the fluid. It only has 20k on it. The filter is done every other tranny fluid change (every 15k)). The truck seems to shift okay (if not just a little firm between 1 and 2 if I put the pedal down). I confirmed that pulling onto I-88. I counted 4 (or 5?) shifts (TC Lockup?) between ramp speed and 65mph. The RPMS stay below 2k when below 65mph when it is in overdrive.
When we got the truck, the tranny was rocking the whole truck every time it shifted with a bang (This was in Dec 2007 at 58k). The GMC dealership replaced a "TCC Solenoid" and the problem was still there. It wasn't until May 08 when I noticed a loose connection at the PCM (one of the top plugs was halfway out). I reseated it and the problem vanished completely and hasn't reappeared since. Do I have a transmission problem? Does this mean it is slipping? When the tranny was still shifting rough, could that have caused damage that I am only now seeing the beginnings of a major problem? Thanks.

 

Newer versions of the 4L60E lock up the Torque Converter in both 3rd and 4th gears (OD).

TCC will disengage/engage and causes your RPMs to flucuate 200/300 rpms.

 

So basically when it is getting ready to go into third or fourth, the TC starts to lock, but since I interrupted it by retarding the throttle as I speed up to avoid going too fast for the road or cops, that caused the computer to get confused and unlock it again and downshift or upshift at the same time?

P.S. Also, in case anyone is going to ask, the A/C was off. That sometimes confuses me with RPMs (and makes it harder to tell if there is a problem) and it makes alot of noise when the engine is at higher RPMs, so if I need more power, I press the A/C button and make sure it is off. Maybe I should add some more oil while I am at it. I added a 3oz shot of it a couple months ago, but since I have to recharge the system once or twice a year (VERY slow leak), maybe it isn't enough in there.