Last night I pulled the valve cover off and adjusted all of the valves 3/4 of a turn passed the noise with the motor running. I don't believe it is valve lash. I have ceramic-coated headers and the #5 primary tube is dulling badly. I think that cylinder is to lean because the truck is getting 12MPG and it has good power. I also checked spark and it is fine. What do you guys think, flat cam lobe, valve guides to tight? I'm going to pull the spark plug tonight to asset how it is burning and the do a compression test. I figure if I get higher cranking compression then any other cylinder my cam lobe is flatting out. Thanks in advance for any suggestions.