Did the problem happen after the engine was installed in your truck? If so, did you clean or replace the fuel tank before running the engine? Sticky valves are most commonly caused by gunk from a dirty fuel tank getting dissolved by fresh gasoline and getting deposited in the valve guides. It usually happens after a couple of warmup/cool down cycles that allow the guides to tighten up. Then shortly after the next startup a valve seizes in the guide and a pushrod bends. You might be able to use penetrating oil and a pry bar between the rocker arms and the shaft to see if all the valves move freely, but the most effective fix is to remove the cylinder head and find the source of the problem. It will either be too-tight valve stem to guide clearance, or more likely, residue from contaminated fuel.
Jerry
