[jdmccright]

I'd definitely have it looked at under warranty. I'd also ask to drive another similar car to see how it SHOULD behave.

Typically when you are driving and let off the throttle completely, only the fuel is cut off. The engine and transmission should continue to remain connected, though if you are in overdrive the torque converter lock-up may disengage. Your engine RPMs may drop some but not all the way down to idle speed because of the engine braking feature. Once you come to a stop (or slow enough to approach the engine's idle RPMs, the ECM will start to feed gas to keep the engine running at idle speed so that the engine doesn't stall.

During all of this, the transmission should be changing the gears to match the vehicle's speed...all unbeknownst to you since the torque converter is the buffer between the engine and the tranny, allowing the slippage needed to make all the gear changes smooth while the car decelerates.

What it sounds like to me is the torque converter is having trouble locking and unlocking. Have the dealer look at it...it may just need a reprogramming, but it definitely sounds like a warranty issue. Good luck!