A friend of mine has an '06 Durango. I believe it has a 4.8 liter and is 4 wheel drive. When she lets off the gas the rpm's jump almost like it is shifting. Any ideas???

 

Possible dirty throttle body or idle air control motor.

 

The Durangos never came with a 4.8L. Its either a 3.7L V6, 4.7L V8, or 5.7L Hemi V8.

The IAC only works when the engine is idling. I'd try the TPS (throttle position sensor) first, common thing to go haywire on these engines after 75000 miles or there-abouts.