First-,,car developed a shudder when accelerating .Mostly between 2/3rd shift. Dealer kept sending me away saying "no code-no fix". About 3rd time in..the mechanic to a ride with me and car finally acted up to prove problem. They tried to take apart transmission....but wound up replacing with remanufactured, I was very happy.

About 2 weeks later I attempted to pass a semi-truck on a 2 lane highway. Depressed gas pedal about 3/4-7/8 to floor and car accelerated almost to redline..but instead of upshifting to next gear....it downshifted at least one gear...drastically revving engine and slowing car. I was shocked and after making my way behind truck I pulled to the side..Car was in limp mode, and engine light was on.

I turned off car for 30 min....and it reset out of limp mode on its own. When I started engine,,I heard a knocking sound,,,like a rod bearing or main bearing. Limped to dealer and asked them to fix. They actually said there was no code so they will look at it but couldn't help. When they test drove it...the engine let go and they replaced engine. Again..I was happy with their service but now do not trust car. Its very dangerous and scary when car downshifts to 2nd or 1st when going 70 or 75mph during a passing maneuver. I decided I would just manually shift car if I had t pass'.

Of course I finally forgot to do this and tried to pass,,,and car violently downshifted during a pass, I tried to manually upshift it but it was stuck until car got down to about 20mph,Traction control was lit again and engine light was on.

Took it back to dealer and they said it finally threw a code,,and indicated that they should change the ECM. They changed ECM and car functioned great for a week or two. Then,,I decided it was finally fixed and tried to accelerate from 60mph and pushed pedal down. After downshifting well and accelerating, car downshifted drastically and raced rpms to well past 8000 and car skidded and slowed. Pulled to side with trac control light on and engine light on.

Took it to dealer who asked me to take it somewhere else after telling me that its my fault that the electrons in the new computerized transmission need time to get to computer and that i am confusing computer. They said you can't mash on gas in new cars.(why the heck did I spend extra money on a turbo model then?)

Knowing that was complete B.S'.....I tried a Buick dealer down the street who told me they don't have a powertrain expert and couldn't help...so I called the GM phone on my owners manual....they opened a case # and and found a Buick dealer that actually works on Buicks.....so we will set up some kind of test drive I hope...because this is really dangerous and in nerving now...not to mention the engine has been over revved several times now and I just wonder how long it has left before it goes again. I told new mechanic if I can duplicate the error...it will quite possibly ruin the engine and be one hell of a scary ride, but he's still in...so here we go. Sometime this week I hope we will do this and with any luck the car will do it when mechanic has his scope hooked up (and we live through it) so I can finally not just get it fixed....but show these guys I'm not imagining it or doing anything unusual to cause it.