I won't dispute the possibility of a worn(or somehow defective) belt as a contributor to pulley squeal. On the other hand, even a properly adjusted belt in relatively good shape can be over taxed. Since you don't have access to pressure gauges, I suggest you check again for restriction through the condenser and radiator. If your tractor has those silly screens in front of either (or both), take them off. Just a casual "look/see" in therewith them in place won't always tell you the whole story. Get an air nozzle with a wand that blows air at a right angle and go over ALL the cooling coils. Using the wand you can force air between the fins and tubes, not just across the front. Spend some time at it, and cover as much area as you can. When I do this, it can take twenty or thirty minutes but can surprise you with how much dirt and fluff comes out. If this is what you find, the belt is probably not the problem.
As a side note, if it were me I'd put the screens on a shelf somewhere, and not back on the tractor. The stuff I find in the fins went right through the screen anyway.
