I have a Craftsman 5.5hp rear wheel drive (917.377792) mower that loses traction in spurts going uphill. It works fine on the flat. I did the push button drive belt thing which didn't help and actually made it harder to manually push through the loss of traction. Even if I do take it in for repair, I would like to know what may be causing this so I don't get ripped off by the repair shop. I'm a woman and it happens!
I would start by checking the drive belt to the rear wheels, and make sure there isn't a lot of grass build up around the drive. Worn drive belt could cause your slippage problems, as well as grass buildup could be preventing the belt from getting a good grip on the drive pulleys.
If the mower isn't under warranty it may be cheaper to take the mower to an independent repair shop and let him look at it. I can about guarantee that sears will over charge you for repairs.
