Had delay in shifting from dead stop, changed fluid/filter-no help. Took to dealer, read code p1811(since this is non-emission code trans manual states will not give dummy lite), recommended replace trans $3000!--no thanks. Read on this forum bout solenoids(aka valves) (thanks to all who posted) and for about $300 in parts and a full days labor with buddy, shifting like new for past month. Here are a few details:
1. Download trans manual from ATSG for $30, great diagrams etc nothing in Haynes/Chilton gonna help(except torque settings for everything your gonna pull apart to get to this).
2. Replaced 4 solenoids in trans, was confused til realized some go by different names with same part #. Basically there is 1 TCC(TorqueConverterClutch) solenoid, 2 shift solenoids(identical, same part #), and 1 EPC (Electronic Pressure Control) aka Control solenoid. Ordered from rockauto, see below:
3. Ran half can SeaFoam for bout 30 mile highway trip to flush trans.
4. Also ordered trans side cover gasket(O'Reilly Autoparts), med duty cooler kit and new motor/trans mounts(may as well do em now)-rockauto
5. Dropped pan n filter. Pulled wheel/hub/axle/strut from driver side after getting car nice n high. Axle puller free rental from Advance. Worked side cover bolts from above n below. Will need to undo cradle bolts for enough play to raise n lower trans. Side cover combo torx and metric bolts.
6. Solenoids easy to match up (by appearance/wire colors) and change. Replaced all 4 since cheap n not worth taking chance after this kinda labor.
7. Installed cooler (did not come with correct fitting in kit, just re-used old section trans line after flaring end).
8. Buttoned everything back up and completely solved problem.
Quantity Return 2003 PONTIAC GRAND PRIX 3.1L V6 Transmission-Automatic : Control Solenoid 1 2