Travis,
According to the service manual, *without* dual rear wheels you DO NOT need to remove the axle shaft.
Now I've never had to remove the rear rotors on my truck (yet), but according to the service manual all you need to do is remove the brake caliper and caliper support bracket. If you've done that and the rotor won't easily come off, is it possible you:
1. Have spring washers on some of the wheel studs? These are installed at the factory to keep the rotor stuck on the axle and need to be cut away before the rotor can slide off the studs.
or
2. Is it possible the parking brake shoes are catching a groove worn inside the rotor? If so, maybe you need to release tension on the parking brake cable to allow the parking brake shoes to retract?
Good luck,
John L.