Speedo pins at 80 when i go about 45 and stays there until i slow down. help

I have an early 99 F350 7.3. When i first start the truck the speedometer is pointing straight down but when i hit about 45 it jumps up to 80 and sticks there until i slow down. At that point it drops back down past 100 and points straight down. I have already Replaced the VSS over the diff and can not figure out what to do next. No lights come on. No OD flashing or ABS lights. Any help is appreciated.