Pull the deck and check each of the pulleys. You have two drive pulleys and two idler pulleys. The idler pulleys are spring loaded to keep the belt tight, and to yield with changes in torque, to save the belt. It sounds as if one or both idler mechanisms are gunked up and are not operating freely. If you have a stuck pulley, that will also heat up like crazy. If you are burning belts you should see some evidence of that level of heat on whatever is creating the problem. Another possibility is that the serpentine belt is threaded incorrectly. Sometimes we are careful about looking after the tractor but forget to grease and clean the mower deck... (inserts admission of guilt here).
