WHATS WRONG WITH MY 7.3?!? 

VSS on the back could be it but there are also speed sensors on the tranny. The VSS is easy to change so try it first.. its on top of the rear Diff.

I wonder if its the vss sensor on the pumpkin in the rear that may be the issue or a bad cluster also get your self torque pro app i just got a early 2000 7.3 that is not so bad and not in to bad shape i prefer it after i sold 2 of my 6.0s and studded for the old 7.3