Viper does this unit have an encoder on mast? should be located on top left chain pulley if i am remembering right. Also it may have 2 controllers. One controls drive and the other is like a VCM. If the VCM was changed out then you will have to program the encoder height read and all parameters unless it is an OEM unit ( which is a pain and done through joystick and deadman switch). If it is the encoder thats "wigged out" then a replacement encoder has to be wired correct as a couple wires will need to be reversed on the encoder or it will count reverse. Been several years since i have dealt with one of these. Perhaps someone else can add more info or be more help..