I just had the transmission rebuild in my 09 Silverado, and when we got it back we noticed that randomly while driving the RPMs will accelerate if we press down on the gas but the speedometer won’t and the truck doesn’t pick up speed. This is usually then resolved by putting the truck in park and then back into drive. We brought it back to the mechanic that rebuilt the tranny and of course they “can’t duplicate the problem” as it only happens very randomly, and not at all consistently. Any ideas?