My '01 7.3 is having some transmission problems, My O/D light is flashing. Trying to go after stopping at a light is a difficult, it drives very sluggish, like its not in overdrive. Scanned it and got three codes P0732, P0720, P0503. I replaced the ABS/VSS on the differential and the problem still exist. This is my first post, so please let me know if i'm posting in the right area.

 

You're in the right area. The VSS that you replaced won't set any of the codes that you have. The first one to fix is the P0720. That's the output speed sensor on the rear of the trans, not on the diff. It's either a bad sensor or a damaged wire to the sensor.