I never said I was going downhill. This happens on a flat road.
I did an experiment yesterday. While driving in 3rd gear at about 3k rpms I let off the throttle and shifted to neutral. The engine stayed at 3000 rpms for a LONG time while I coasted down the road. Finally after about a block coasting I braked and once I got to about under 10 mph the rpms started dropping to about 1200.Weird!
I've read something about "Throttle body resonance" which seemed to be a problem and caused a recall.