Don't know anything about 4520, but on the 3320 you do not need to take the tractor to the dealer to calibrate the throttle position sensor. For the most part you sit on the seat engine off, toggle some switches, move the throttle lever, and take some readings. You then loosen two screws at the sensor, slightly turn the sensor, snug the screws up and then take the readings again. Do that until you have it within specs. The worst that can happen is that the sensor will not fall within specs and it may have to be replaced. I believe that is all of two wires and two screws, if not, that is close.
To do a full drive train calibration requires all tires to be off the ground and be run at full throttle, be carefull with that one. Have good jack stands and some clean underware around to change into if the tractor slips off the stands.