Yes, as a66coup289 said, make sure you're using the correct size belts.
Also check the belt routing, paying particular attention to how the belts come onto the pulleys. Sometimes you can encounter a situation where an idler pulley mount is bent or out of position due to a worn bushing in the tension arm pivot and it causes the belt to want to ride up onto (and out over) the edge of the pulley (particularly with the backside idlers).
As for the 446 not staying in float, on the back end of the TCV (travel control valve) there should be an end cap with a couple of spring loaded detent balls (under small screw caps) that hold the lift spool in the float position. You'll have to do some disassembly to check for worn or missing parts (preferably working somewhere that the small parts won't disappear into the snow, dirt, or a crack in the floor if you accidentally drop any).
The 446 drive lever not wanting to stay in position is likely due to a worn neutral safety switch assembly. Most of them (until the later years) have a series of small notches in the plastic body of the assembly that make contact with a metal pin that's welded to the travel control lever up under the dash. When they're in good condition, those notches help hold the travel lever in the position you select. But they wear down with use and eventually get to the point where they no longer hold.
