2000 Monte Carlo, hard Shifting when warm

Here is my problem. When the car gets warm the transmission goes into hard shift mode. I have hooked up a scanner--no codes even if it's running. I'm aware of the problems w/tcc valve but does this occur when there is no code thrown? Or do I have a solonoid problem which occurs when it gets warm?Or what eles would do this.I've run it up to 60 and stepped on the brake. Converter does not unlock. Any good suggestions?

what's the mileage? have you done a trans filter change if over 50K?

Car has about 100000 miles on it. Has had three changes of fluid and filter, I do my fluid changes about every 30,000. At the last change it took longer(milage) before it started again.

I know this will sound strange, but other people have done it in other GM w-body forums with good success. Unhook your battery and leave it unhooked overnight. It seems to have worked for many people with hard shifting transmissions. I've never tried the trick myself, so I'm going off what others have said. I wouldn't mention it, but the people that have said it works are reliable sources, who were amazed themselves that it worked.

I have already done that. It seemed to work short term but it did go back to the heard shifting after driving about!

I had this same problem in my '99. I had to replace the pressure solenoid in the transmission.