spedo not working od light flashes

[mustangmatt89]

so coming back from work last night my spedometer started to jump around and then my od light flashed accompanied by some very hard shifts? The tach was still working fine and have a new tach sensor on the 7.3 idi but where should I start looking for this problem? It does it sometimes and then goes back to normal, and shifts rough like it did when my tach sensor failed. oh and the truck is a 93 7.3 idi banks turbo with a e40d trans

 

[flareside_thun]

Sounds like the VSS in the rearend took a crap......easy as hell to change out.