Hello, everyone!!! I'm new here, hoping you, guys can advice me little bit!
I read a lot information, but, unfortunately, couldn't find the answer.
The problem for last 5000-8000 miles: Transmission was shifting really hard between all gears, slipping on first gear from start for couple seconds then getting "kick" and van starting move normally. All symptoms when tranny is hot(after 20-25 min drive).
What I've done: 1000 miles ago changed transmission fluid and filter. Fluid pan had normal "mud" around magnet without metal particles. I got good improvement- all "kicks" got much more lighter. Anyhow few days later put my van for diagnostic at transmission shop. Result of diagnostic: P1811 and from 2200-3000$ for rebuild tranny . Took van home, ordered TransGo Shift Kit and 300 miles ago I installed it by myself(of course again changed filter, fluid).
Result: Shifting perfect between all gears(cold, hot - no difference), but slipping on fist gear, just when tranny is hot, almost every second start, yes, some starts is perfect. If put lever to D1 no slipping.
Please, advise me!

sounds like the transmission pump is getting weak, most likely time for rebuild or swap out

also, check the transmission modulator vacuum line, on the front of the transmission, follow the vacuum line from the modulator up to throttle body.

The vacuum T on the side of the throttle body usually cracks from heat and needs replacement, this will make transmission shift hard, as in dumping into gear instead of smooth shifts. also engine will be idle a little fast due to vacuum loss

If that T needs replaced, it is available only through GM, most dealers have them
It'* also available online for a few dollars

We can look up part number if needed

Disconnect battery to reset idle after install

hope this helps, and was just a thought....

Thanks! I'll check it tonight, and let you know.

The P1811 generally is the PCS solenoid in valve body.
Further read...
2002 Buick Regal with P1811 code - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat

Soft Ride, thank you for reply, but i already instaled Shift Kit. I'm having now just one issue: slipping from start on 1st gear when tranny hot.

Zach if you are intending to keep the car, slipping, black material found, indicates clutch pack wear. Time for a rebuild by a reputable shop. It may be best that they replace the entire valve body with updated components & all new electrical as well. I would also consider a new torque converter, to ensure you are good for the long run.

Today i measured the line pressure after 20 minutes driving in town.
P, N, R - 60-60 PSI
D4, D3, D2 - 40-45 PSI
D1 - 120-130 PSI.
I thinking it is bad, but how bad? Of course i dont want spend 2 or 3 thsousand $ for tranny rebuild....

Pressure control solenoid been replaced, no slipping any more!

thanks for updating your fix