I have a code for a tcc problem, which I believe is 39.
In the morning, when it is nice and cool, when I start driving, the TCC comes on like it normally does at 60-70 kph, and when the car hits 80, 4th gear is engaged. It does seem to get lazy engaging, until 4-5 mins later, the TCC is gone all together. I do have 4th gear however...... For another 5 mins. Then it is gone, and when I am cruising at 100 kph, the engine revs anywheres from 2500-2800 rpms, instead of 1800. This is quite a waste of fuel.

The fluid is a little old, but still in good shape, and it shifts great, no slipping.

Using Identifix, someone says that 4th gear will be inhibited if the TCC does not work?

Sounds like I need to replace the TCC solonoid in the tranny? Its 50 bucks for one, plus a little labour on my part, lol. Question is, are there 2 solonoids in this tranny for the TCC? One to apply the TCC and a PWM to control line pressure?

Anyone ever have experience with this issue? Thanks

I take it that since you are posting in Buick you are referring to your 93 Pk Ave?
Often the solenoids, valve body check balls etc...get gum & varnish build up, causing slipping or No lock up. Good transmission maintenance fluid & filter (once every 35k miles) goes a long ways in keeping transmissions healthy.
Before I would replace anything, I would put a full can of this into your transmission fluid, drive it for about 500 miles and see if it improves.
Trans Tune - Sea Foam Sales Company
There generally as far as I know are 2+ solenoids. I would want to refer to the FSM for your vehicle.
On my 4t65-e I used the Trans Tune, things got better fairly quickly, it was harsh shifting when hot only, and lessened once Trans Tune was in.
I then also installed a Transgo spring & spacer shift kit into the accumulator body accessible for the pan drop area, and replaced the filter and went to the best GM trans fluid Dexron VI (6) Nice stuff!