When you are driving the truck the abs light will suddenly come on and the speedometer will jump back and forth anybody got any idea what is going on with this truck?

 

Sounds like the ABS sensor in the rear diff is on its way out......

 

i have changed the abs sensor and it didnt change anything

 

I believe that you are experiencing a classic VSS failure. Not sure where yours will be located. In my 2WD it was screwed into the rear diff, up on top.

Mike

 

Follow the wiring from the sensor on the differential, to where it crosses over to the frame and heads forward. Have seen several harnesses get beat up by gravel where they are exposed. The wires can get torn open and corrode. Also have a close look at the terminals on the sensor connector for corrosion.

 

ok ill trace the wires and check the connectors and see where that gets me