is it a manual or an auto?
also check the emergency brake and make sure it engages the little switch.
if it is a manual there is a switch on the clutch that works to ways one way is all the way down to start the truck and the other is all the up to allow the cruise to engage. pull the switch out and check it with a um i can't remember what the exact name is but it's on a volt meter and it beeps check to make sure your switch is working