I have this problem with the Bonn, when it is running about 1500 - 2000 rps and building speed it feels like the trans is shuttering. I cannot tell though if it is really a trans issue or if it is a engine/trans mount letting the engine surge forward and backwards. I did scan the computer for codes and found 1 in the history file p1811 max adapt long shift code... I dunno really what it means but the car has 135000 miles on it, the fluid is very clean to look at, it has no oder of being burnt.

it'* a series 2 non */C engine but I am not sure of the trans model or ratio. I love the car and will repair it as needed but i'm wondering if anyone has a idea of the code or a similar issue. What is a GM rebuilt trans price on one?

Sounds like the pressure control solenoid is going out and the p1811 pretty much confirms it. Your transmission is a 4t65e and this is a very common problem with them.
4T65E Common Problems

interesting info... but like it said high mileage could be a lot of things.. :( is there a code someplace to see what transmission / ratio is in my car? pretty sure it is a 4t65e but I havent worked on this since i bought it.

The build codes are under the spare tire cover.
2.86 Ratio Opt FQ3 ident PAB
2.86 Ratio Opt FQ3 ident PPB
3.05 Ratio Opt F83 ident PBB
3.05 Ratio Opt F83 ident PCB
Last time I checked the Dealer quoted me 1600.oo for a SERTA transmission but it comes with a 5yr warranty

is that a rebuilt or new one?

Rebuilt but will factory updates

I would still try the PCS before I replace the whole tranny.

Before you go to all the work, you may want to replace the trans mount, install a shift kit and convert the trans fluid from DEX III to DEX VI.

I had the same problem you are describing, getting worse in 2008, 88k miles. I did the above, and am now at 190k miles and have not had to repair or replace the trans. Cost was under $150 (shift kit, DEX VI, trans mount, trans filter) , under 3 hours labor, and it is fairly easy to do. I learned to do it right here at this forum from Dan Thurs.