Marcus,
Is your garage heated? If so, I wonder if the warm metal contributes to the issue of snow/slush sticking to the insides of the blower.
Also, I believe the 5/8" of clearance between the fan and housing is excessive. My Farm King (Buhler) starts at about 1/2" at the 12 o'clock position and tapers down to about 1/4" as it approaches the chute at about the 9 o'clock position.