HELP... bought used Yamaha 450 Kodiak 2006, if I try set the diff lock into 4wd, the machine starts to run really rough and sputter as I try to accelerate, idles fine but no go in 4wd diff lock, runs strong in 2wd , I can hear the servo box doing it's thing , I suspect electrical problem but have no idea really, anyone out with similar problem and solution? diffs front and back rebuilt gear gaskets etc,