Do you know if they put a different transmission in the truck? There are small gears in the transmission that can be changed based on tire size changes and rear end gear changes. See
http://www.transmissioncenter.net/sp...n_______va.htm
This may or not be your issue but if the signal from the VSS is good, you may have to check to see what gears are installed in the tranny.
//2000CAYukon