Craftsman 10.5 hp snowblower in gears 1 to 6 creeps along very slowing with no real power in the wheels. Same for reverse.

Check the shifter linkage from the handle down to the units transmission. Show not bow or bend. Some blower have a two part linkage held together in the center with 2 screw or bolts, drop one bolt and the linkage bends

Hi,
Just to add Craftsman machines use a drive disc whose rubber perimeter can wear out. With a model number you can try this link for a parts breakdown.
Ordertree.com | Lawn Mower Parts | Emergency Preparedness (http://www.ordertree.com/modelinfo/MURRAY/63.1.html)
Peace,
Clarke

I had topped up the oil and overflow had dripped on to the rubber,maybe the previously perimeter.