hi guys. if i'm reading this right then i'll bet it's the gas gone bad as stated above. had this happen to me on a 5.7, had 3\4 tankof fuel in the truck and had some old gas (that i dn't think was that old) so i through it in the tank and drove to work the next day.drove to work the following day and on the third day went to start the engine and all i got was a very bad noise. (stuck valves. very costly 2 gal's of gas. if you don't drive that mush maybe you could try to add something like (sta-bil) to the tank and that should help in the long run.ithink that you are going to have to pull the heads to fix it right good luck