Originally Posted by 96R50

It sounds like your starter is good. How is your battery? Do you have a DVOM attached so that you can see how the battery is handling the load of the starter? I suggest taking a reading at the battery while trying to start the truck. Then take another reading at the starter to rule out a corroded or faulty lead to the starter. If the battery is dropping to <10V while the starter motor is engaged you really should consider a new one.