Make sure everthing is moving and nothing is binding. I had to take my wife's rear skid completly apart to clean everything. Rust builds up in all of the pivot points and makes the rear suspension tight. Grease all of the spots that has fittings. Even when everything is working as it should, it still shouldn't come all the way up. With me on my wife's XLT Sp, it still 4 inch's down from all the way up.
The only other thing it could be is the shocks. One of my friends had his shocks rebuilt, but he got them back in worse shape than when he sent them in.