Sounds like a bad motor. Had it happen on a Rainier. My problem was there was dead spot(s) on the motor and once it got going it was fine because there was enough contact for it to keep spinning. But once it stopped, like roulette it would sometimes work usually not. Then I would hit a bump and it would move enough to start working again. I also think it was not pushing as much air when it worked, which would make sense if only part of it was working.
I would recommend not getting the cheepo motor replacement as they tend to be noisy for about a year (ask me how I know). I thought there was a problem with the new motor because it wined, the parts store exchanged it, only to learn it was the cheepo motor contacts that were not broke in properly.