Hello all. This is my first post. I bought this 2005 grizzly 660. Just put a plow on it. Rear tires only spin. The red 4wd selector on the handle bar is pushed in and only rear ties spin. When selector is out same thing. When I move over the diff lock selector and try to engage that it runs really bad. ie misfiring. Maybe elec issue? I put the bike on jackstands to verify that rear tires are only spinning. Any diagnostic help would be appreciated.