I have a 2006 monte carlo lt3 with only 37,000 miles, so the problem starts when the traction control would engage. then on the dash it will say servive traction control. right after that the trans will act up,it will shift hard and very fast.i was told by my dealer Tom Henery Chevrolet that the shift control module needed replace. they kept the car over night cause the module sat inside the trans. Got the car back now the traction control and the trans shift find. But now from time to time when your at 60 mph or higher and punch it the trans down shifts nice but the car does not seen to have a strong pull its like the trans went into default. And other times you punch it that baby takes off, any ideas what it is? Or it could be this me.

 

I would have to test drive that and experience the issue it's having to give you a recommendation but, take it back to the dealer and tell them it is not right and maybe they will test drive it and find something wrong. Or better yet take the dealers tranny tech with you and drive it yourself to show them the problem.