Need help understanding automatic transmissions

Working on a 1997 GMC Sierra K1500 305 4l60E. I had the code read and it said the TCC solenoid wasn't disengaging so I bought what gm calls the tcc solenoid and it had some electrical backwards, so I decided to put the old vavle back in because what I bought wouldn't fit correct. I also figure now that it ain't the solenoid that needs replacing. Anyways, after I pulled it out of the shed it continued to shift like crap, hard shifting, almost stalling when stopping, no power because of early shift and no tcc slip to allow for acceleration as well as not unlocking when hitting the brake. After about 15-20 miles of pulling the trailer(approx 4000lb) it started to work PERFECT. All shifts were smooth, correct shift timing, it never slippeed or anything. It worked just the way it should all day long. It does this everytime I pull the trailer. No matter how terrible it was shifting before it snaps out of it and acts perfect. It will work good after as well for a while but reverts back to hard shifting. It might randomly start working properly for 10 minutes and then start shifting too early and too hard again. It really seems to get worse in the cold. I've replaced the fluid twice. The fluid didn't smell burnt at all and was slightly darker red then new fluid after 25000 miles. The magnet had about 1/8" of crap on it the first time and a bit on it when I changed it again after 2000 miles. When it's not shifting properly it will shift from 4 to 3 but it won't unlock first, it just jumps to thrid with a hard shift ,and when it shifts back into 4th it doesn't shift into 4th with the tcc unlocked and then lock up, it just stays locked and shifts. The transmission has a 11"x16" external cooler without a cold weather bypass.Sorry for the long speil about this. I just don't know what's wrong with it anymore. I can't figure out what is going on with it that it works so well with the trailer but runs to badly without it. Thank you for any help.

You must be sure to use exactly the correct fluid in this transmission. If you have put the wrong fluid in, you must drain it all and refill and go by the dealer and have the correct parameters reinstalled in the computer. Don't know this to be true , but this is what I am being told. Know it is true on Dodge and Ford, from experience. Also know that all three manufactures transmissions were developed following same design.

What code did you get. I build trannys at a gm dealer for the past 12 years. P1870? or P0741? p1860?

none of the big three trans are the same design at that time. completely different. Althought, the new 6 speed transmissions i am repairing at the GM dealer are shared with Ford. I think the Ford Edge has the same trans design as the front and AWD Tranverse and Enclave, Acadia (6T75 and 6T70) When i was at training we compaired pieces from a Ford 6 spd and GM and they were the same. The 4L60E is nothing like a Ford or Dogde light duty 4spd auto.

I can't remember the code #. One code was for TPS and for the other it said something like 'TCC solenoid not disengaging' or something to that effect. On the TPS it might have said something like 'out of range' but I just can't remember. I really should have kept the codes. I replaced the TPS but it really made no difference.

I used Dexron III ATF both times. I considered using Dexron VI but decided to stick with III for now.

Well tps codes will make the trans shift all over the place. Dex 3 is just fine. dex 6 is waste of money for normal truck like yours. You have something going on with trans and not enough info to diagnose it. Your putting the cart ahead of the horse with fixing the trans if you don't even recall the trans code?? magic fluid won't save this. dex 6 is a synthethic fluid used since 2006 in GM and last longer under heat and stress. find out code and that will help. these trans are very easy to repair and diagnose, but starts with the right info.

For one thing, it sounds to me like the converter itself is not releasing (probably dirt and filings holding it locked) and the 'puter sees this as if the solenoid is not working and sets the code when it's doesn't "see" the desired "slip" ratio between engine speed and TIS speed (transmission input shaft speed).

Humor me,

Unscrew the electrical connector and see if it is full of tranny fluid.

Allan

Is this electrical connector on the outside or the inside?

Outside, passenger side of the trans.

The wiring loom plugs into the transmission from the top down behind that large round actuator housing and is held in place by a large round nut affair (water pump pliers). :>)

Kinda hard to get to as it's in behind that tin heat shield that you have to remove first via some little bolts.

I use a little mirror and a flashlight to be able see down into that cavity on the transmission.

If it has fluid in it, use some brake clean and compressed air to clean both sides of the connection. Get it clean and dry.

Then, put 'er all back together and take the truck out for a drive to see how it acts.

Allan