Quick shifting (sometimes) after warmed up

[ovel2clock]

2000 Grand Prix SE 3.1 I've "inherited". From a cold start, shifting feels OK. Then at some point after being warmed up, the car goes into what I call "indy car mode", where it shifts immediately. Doesn't happen every time, but often enough. Turning off the car and letting it sit for 10 minutes seems to reset things.

Any idea where to start? No CEL or codes being thrown that Torque can read.

[FordMan77]

What kind of condition is the fluid in? Is it nice and red or brown/black? My 00 GT does this occasionally. Figure it's the PCS going bad. Your average code reader cannot scan for trans codes. Take it to a trans shop or dealer and have it scanned and see if any codes pop up.

[BillBoost37]

Can Torque read P1811? That is max adapt shift. If the pcm see's something with the trans as being bad, it'll jack line pressure causing harsh shifts and this code is stored in history, but not current. Meaning, cycling the ignition would reset it, and a scanner may not find it based on having turned the car off.