Audi A4 2003 transmission slip (CVT type)

My Audi A4 cabriolet 2003 has been having apparent transmission slippage problem since about 32,000 miles. The dealer can't locate the fault and claims the computer logs show no fault. I have repeatedly noted engine RPM's rise but the car doesn't accelerate--twice from stop lite five times from 10 mph roll.
Car is covered under "Fidelity" extended warranty. Dealer seems to be nervous about undertaking repair only to be denied by warranty. The warranty was purchased from same Audi dealer in conjunction with purchase of new A3, but was separate transaction. Any thoughts??
My inquiries about changing transmission fluid were refused as the system is closed and not changeable w/o new transmission install.