I don't have a good source at Cummins, but do at Caterpillar. And the answer is as long as the engine is above idle speed (we are talking about automatic transmissions here, since that is what RV's have) no fuel is injected.
If someone has a reliable source at Cummins (not just a kid who answers the phone, would certainly like to hear from them. Again, the question is when you release the throttle at speed, is any fuel injected?
BTW, for any of those with Silverleaf or ScanGauge D, within seconds of closed throttle, instant MPG goes to infinity (or on my ScanGauge D to 999.99 MPG).
Yes, this is more a curiosity question than one relevant to how we drive, but interesting none the less.