It probably(as my truck has done TWICE) has too much torque on the tranny. ******Do the following steps safely. Jack up the rear end and block the front wheels, and set the parking brake. Then, either hit the starter(DON'T START IT!!!) or you and a friend turn the (rear)wheels forward. This should take the torque off of the tranny and allow you to shift into neutral. You can also turn the engine by hand. I'm not sure about this, as I used the starter, but you may need a third person pushing up on the lever to get it out of gear by turning the wheels.
