'93 TCC issue

'93 Custom with 3.1L and 114,000 miles. Tranny in this car works and shifts great except for one minor issue. The tcc doesn't unlock with steady/increasing throttle at highway speeds under increasing load. Two examples: first I'm traveling at 50-60 mph and start up a hill. As the load on the engine increases, the car will shudder. If I lift off the throttle and immediately back on, the tcc unlocks, revs go up and it's smooth as silk again. Second example: with cruise on 65mph start up a steep hill. Speed will reduce to 60, tcc doesn't unlock and when the cruise pulls the throttle far enough, it downshifts hard because the tcc is still locked. Tcc should unlock first under the increasing load before tranny downshifts. However, if I manually downshift to third when starting up the hill, the shift is smooth as silk. I'm assuming the tcc solenoid is ok as it locks and unlocks just fine most of the time. But it's not getting the proper unlock signal when load is increasing. Is this a fluid pressure problem? Would just changing the fluid help? Also, which tranny does this car have?

The issue hasn't really concerned me much as I know how to work around it, but I'm planning on selling the car and it's a bad thing to have happen during a test drive. Tends to scare off potential buyers.

A scan with a high line scanner will look at whether the solenoid is being commanded by the pcm, the tps could cause this as well as a lazy solenoid.

A scan with a high line scanner will look at whether the solenoid is being commanded by the pcm, the tps could cause this as well as a lazy solenoid.

And how would I accomplish this?

I threw a can of Sea Foam Trans Tune in it on Sunday and drove around a couple days. Yesterday I changed the fluid and filter and took a trip over 320 miles. Although the tcc still doesn't release under the conditions mentioned in the original post, the shuddering is completely gone! I drove up the hill by my house where it always happened, and nothing. Smooth as silk! Shocked the hell out of me - I never expected that would help!

And how would I accomplish this?
Most good repair shops or a trans shop can do this.

Most good repair shops or a trans shop can do this.

I would need a way to do it myself as I'm selling the car I'm not about to start paying a shop for diagnosis. Especially now that the shudder is gone, I don't really care anymore.