99 Ram runs bad after overheating.

Hi everyone I am new here and trying to help a friend. He was going down the interstate and his 99 ram with 5.9L overheated and now runs rough with no power at all. We found the reason for why it overheated and replaced the bad radiator. Thinking moisture got into his cap we replaced it as well as the rotor, wire and plugs but it didnt fix it. We know about the wire routing issue and followed the tsb routing for them but that did not work either. Before the truck overheated it ran fine so we are at a loss as to what is going on. I am hoping someone might have been in the same situation and may be able to help.

blown head gasket? warped head? try a compression test see if all the cylinders are the same