When considering average range of operation, 3100 actually is high RPM. Most engines that aren't designed for spirited driving redline between 5500 and 6500, and you're halfway there... of course, you idle 1/6 of the way there.
Imagine you're driving a large diesel - you're engine braking at or near redline. :P
So, just to clarify - make sure that you shift somewhat abruptly, so that the RPM don't have to go back up while you're letting the clutch out. Try shifting without the clutch, if you're comfortable doing so.
I'm thinking that the ECU will think that you're just slowing down, and keep it in DFCO mode, unless it's still taking info from the VSS - at which point it may think you're crazy and:
