Since the dealership put in an Optima battery on long trips I get a reduced engine power message and a service traction control message. When I get where I am going I turn off the engine for a few minutes and everything resets and for about 15 more miles it works fine. Then the message again.

I took the car in to the dealership and they said they had a notice on the problem and put in a new throttle body. I have not had a chance to test it yet but has anyone else had this problem? It is a 2005 C6

I haven't had this problem with mine but a friend of mine did exactly what you did....installing a new battery. After much guesswork at the dealership they finally determined it to be caused by the tachometer relay of all things. I hope this gives you and idea of where to look to cure the problem.