Hi, guys, sorry I didn't get back to this thread. If I weren't 't such an idiot about all things technical I could probably explain it better. Riding along, the bike will suddenly go into a lower (less resistance when pedaling, less power per stroke) gear, the chain slips down one level on the rear sprockets. Hope that makes sense? Anyway, when I first got the bike, after about a week this started happening, I took it back, the tech at LBS said it was due to the cable stretching as it got broken in. He did a quick adjustment and viola, no more problem. This recent bout started after I took off the rear wheel to fix a flat. So, I undid that - I took the wheel off, cleaned and lubed the chain, etc, and so far, no more problem. Maybe something was just a tiny bit out of alignment? See why I wish I weren't such a mechanical idiot?