Stalling in reverse

I recently purchased (as in LAST week) a 2003 VW Jetta 1.8 T (with tiprtonic), 57K, and everything seems to be in good working condition. I've noticed though that usually when I put my car in reverse, it seems to feel like it's going to stall (and one night it did!!). I've taken it back to the dealership(not a VW dealership- but a very trusted and reliable one) and they say they can't find anything wrong....(it's even still under an extended warranty)-- any ideas of what could be causing this sensation and causing the car to stall in reverse?? PLEASE HELP!! I'm really worried...

If there is anything wrong and you have an extended warranty, why dont you bring it to a vw dealer! It could be so many things..

I just filled my tank with Premium gas (not sure if the dealership had filled it with Regular, so i ran it until it was empty)- someone had suggested that might fix the problem. Amazingly enough it does seem to be running much better and I haven't encountered the stalling prob (except 1 time the first day I filled the tank with premium) since. If I still have the problem i'm of course going to take it to a VW dealership. Thank you :)

VW requires 93 (or 91 if you cant get 93) octane fuel on 1.8t and vr6