I've had plenty of experience with skipping problems on my mid-drive. I'm pretty sure it's not your motor. You may have damaged a tooth on the cassette or your chain's stretched (7-months?). I've been pretty rough on my bike, but I've come to understand its drive-train idiosyncrasies. I'm heavier than you, so the abuse is magnified. Between tooth-wear, chain-stretch, and derailleur-bashing, there's a fine balance to be found. I'm not even going to factor in my proprietary front-cog which I'm finally getting around to changing this month after a year's riding.
This all said, I find that when I change my chain, I also need to change my cassette, or at least the highest two gears as they'll wear much faster than the rest. Provided the derailleur is tuned properly, and nothing back there is bent too askew, refreshing my chain/cassette combo every season has solved my EXTREMELY annoying skipping problems.
Thanks Fitzy, I really appreciate the feedback!
