For any of us who have experienced the hard/lagging shifting in our beloved knights.....let's put it to a rest:
Peoples Transmission: P1811 - Maximum Adapt and Long Shift Mode Chevy, Pontiac, Saturn, and Buick Front Wheel Drive Vehicles

Autozone results:





Now.......uhhh help? (Opinions, solutions, mechanics, etc, etc.)

 

According to the link you posted it could be any number of things. The Pressure Control Solenoid, a blockage in the valve body or even low fluid just to name a few. I think you could try to change the fluid and filter and them make sure the level is correct and see if the problem is still there. I will say this, My Venture had the same problem for 5 years and I never did anything to it and it was still working. Every once in a while it would take off kinda hard but then it started doing it I would pull over and shut it off for a minutes and restart it and it would be good.