ok these spark plugs are non adjustable which means they are pregaped and do not need to be gaped due to the reason of damaging the spark plugs. this is a copy from ac delco for your truck. hope this will help. and always replace using ac delco parts.
check the plugs for a crack on the ceramic portion of the plug. you can use a spray bottle with water in it and spray on the wires to see if you can locate the cylinder. also is the check engine light on?
but yes the ac delco rapid fires platinum plugs are gaped at 60 and should not be regaped.