had a problem such as yours with same motor, turned out to be water in the hub motor, popped motor case open and drained, let sit overnight and has been running perfect ever since. that was a yr ago. May not be ur problem but an idea anyhow.
Just got a watts up meter installed today. was great to find this thread. my 1 trip #'s are as fallows
efficiency: 33wh/mile
Speed: 20-25 mph avg
Grade: mostly flat, couple downhill grades
Pedaling: just to get started, seems to be easier on the bike
bike: norco mtb w/comfort bike style tires...