i have a 97 park avenue with 70,000 on it no supercharged, its been running fine little bit of a hard shift everyonce and a while, but yesterday the trans started slipping bad. if you let it sit for a little while and cool off it will go right into gear and shift threw all gears fine even reverse untill it gets warm then it loses everything including reverse also but will still go into park, it did have a little whinning sound from the trans and there is no leaks at all, the fluid is a little dark more brown grayish color than red doesnt smell burnt, also had a p1811 code that would not trigger the light in instrument cluster, i think i have stated every issue it has i dont really want to tear into the trans if i have to, i was wondering if it was a possible pressure control solenoid/valve or if anyone else has heard or experienced this same issue, thanks for the help

https://www.gmforum.com/obd-ii-trouble-shooting-153/p1811-288584/

Sounds like it could be a bad EPC

While the EPC is the culprit on the 1811 code.. the whining and no gears after some time sounds like a starving pump. Or the input piston seal that is known for wearing out.

Won't move in gear (note the debris in pan)
http://www.tripleedgeperformance.com..._any_gear.html

Whining (which is also starving pump)
http://www.tripleedgeperformance.com/Whine_noises.html

P1811
http://www.tripleedgeperformance.com...ft__P1811.html

Hmm, how about a blown channel plate gasket?

Not as common. Could be though.

There would be fluid coming out of the vent on top of the transmission if that'* the case.

Right.. OP didn't mention that. Yet.

yea no fluid coming out the vent it will run perfectly fine until warm then it will basically act like going into nuetral in all gears doesnt pull at all, let it sit a few mins and you may be able to drive a mile or two and then repeats the same pattern

Cory...been there, done that. Drop the pan...man.. lol

Take puictures of what you find.