From my last post, http://www.g8board.com/forums/showthread.php?t=21227 she's going back to the dealer for the third time.

Sunday I took her for a 75-mile road trip. Failed. This car cannot be driven on the interstate. All it is good for is local driving. Replacing the tires did not solve it. What is weird is with only 1/4 distance to go to reach my destination the vibration returned and it was present all the way home. If the rotors were found to be out of round as a separate issue, I wonder if any of the bearings or rims or something might be out of whack. I have a feeling this is something that cannot be seen by the naked eye and that's the frustrating part.

Aside from the above, something new happened tonight. At a red light, she started mis-firing. I thought she was going to stall. The V6 does not have Active Fuel Mgmt (AFM) so that isn't it, but it gets better. I get on the highway and just as I am at the point to merge into traffic, the display on the Driver Information Center (DIC) goes blank and appears to reset (not the initial System Check that occurs at engine start up). It then displays the transmission status and tells me I am in Park while going 45mph. WHAT????? I almost $hit expecting the car to come to a screeching halt. The DIC goes blank again, appears to obviously be confused, resets again, displays the transmission status, again showing that it is in Park (umm, no) and then returns to normal. I run the DIC in combo standard/trip odometer mode.

I'm ready to drive it through the showroom window or drive it off a cliff.

Check the Lemon law in your state...

I won't speak on the vibration issues.

What was the code. At least that will tell you which cylinder is misfiring.
That can really narrow things down if in fact that is the case.
Just as an educated guess, it sounds to me like you have a bad ground somewhere. Possibly even a bad ECM.

What is weird is with only 1/4 distance to go to reach my destination the vibration returned and it was present all the way home.

Likely explanation is that a wheel weight fell off.

Unlikely explanation is a lump on tire from slipped internal belts.

I had a vibration issue and they turned all the rotors. While they were doing that, they found a defect in the left front wheel bearing and replaced the hub bearing assembly. My vibrations have gone away but I feel it every so often. I think I'll get all wheels balanced as I received a $100 Voucher from Pontiac for all my problems with my radio.