2002 Beetle Turbo Transmission/Overheating issue

We have been having a problem with our 2002 vw beetle turbo. My
girlfriend drives in crazy bumper to bumper traffic for around and hour
and a half daily. On several occasions, the beetle will act very
bizarre. It won't upsift, shakes, and acts like the brakes are on and
the transmission isn't functioning properly. When we turn off the car
and restart it, the problem goes away...almost as if it has been reset.
The dealership has NO IDEA what is going wrong...they have been unable
to replicate the problem and left us in the dark. The last time this
happened, the car was being driven on the freeway...the car wouldn't go
faster than 10 mph and was at around 6000 rpm. Any ideas???