This site is very good, as I seem to be having more car issues pop up over the past month than have in the past several years. My '00 Impala 3800, 228,000 miles, literally just started having a shuddering feeling starting off from a stop and also intermittent stumble on the highway like someone turned the key off for a split second and then turned back on. I had the dealer plug into their computer to actually see what is wrong since Autozone had no check engine light as guidance. $107 later for a diagnostic fee revealed P1811 and quoted over $3,000 for a new tranny. A very good local mechanic suggested dropping pan, replacing filter and adding 24oz. of Lucas trans. additive and run it. The car is in otherwise very good condition and runs very well. I've replaced the trans. filter every 50,000 miles like clockwork as PM. Any guys out there know of ANYTHING I can do at home short of having it rebuilt? I replaced the TPS as a Buick 3800 forum pointed out as a typical cause of my symptoms, since the 3800 is a Buick design. The TCC was not the problem they said, but the TPS was. That did nothing but cost me $44, but it sounded logical. Thank you for any advice you can offer.