91 Caprice Please help speedometer issue VSS replaced still persists
 

This is for my step dad he doesn't have internet and wanted to know the answer to his question after searching for a while still couldn't find it so I figured this would be the place to ask.

Situation- 91 caprice when it starts its fine when it moves about 5 MPH the speedometer and odometer work but the speedometer goes up to 80 MPH at walking speed. When you start to go faster then that the speedometer and odometer both go out. He already replaced the VSS and it's getting voltage he said. Also already took out the I P and cleaned the connectors. Any help would be greatly appreciated!