It was fairly new and all of a sudden the trans slipped...and it happened periodically for no reason!

The dealers stated they couldn't replicate the problem...although they never drove it...arrived on empty left on empty and not 1 mile was put on to check and see. I called Onstar when it happened and they couldn't see anything happening...this happened maybe 5-7- times...it is a new car for the cost the trans should not have a problem