Ya know I never understand why people try to figure stuff like this online when they have warranty.

 

Because if the dealer can't replicate the issue there will be no fix. Trust me I was the quality control guy at a Jaguar store and the compliant would be "don't know, just dies and I coast to the shoulder. Then it starts right back up??!" Also was a service adviser at a Lexus store. Not as many problems there but that was when they first came out and all of the cars were still under warranty.

 

Since the GMTU install with the auto trans in "I", Comp mode on and an aggressive start it will sometimes slip clutches between first and second. One time with a VERY firm shift in to second just like a "shift kit" was installed. The auto is near the limits of torque capability with the GMTU and I expect that if I don't treat it nice and learn to work the throttle properly under hard acceleration the tranny will blow (or snap a half shaft). I know this does not answer your question just letting you know you are not alone. Oh, I have 45k miles and counting.