How can I fix my Craftsman Lawn Tractor Model #917.255520?

The deck on the mower appears to be too low. Even on the #6 highest level, the deck is still only about 1" above ground level. On a flat surface(driveway) the deck contacts the ground at about the #3 mid level. I can only cut at the highest point. Anything lower or closer to the ground and the blades want to lock up. The mower cuts unevenly, and the vacuum system does not work properly. I read the owners manual about the adjustments and leveling the deck, and I have leveled the deck. However, it appears to me that the entire deck either needs to be raised or the lift lever needs some type of adjustment. Any help or insight would be greatly appreciated.