If this is strickly a pullin' truck i'll assume you have hi-comp pistons. Iv'e never seen a solid cam with that tight a valve settings. Could be when at full operating temp. the valves are hanging open a little. Just throwin' out a idea?
THis is why i urged him to do a compression check. If valves are hanging open he will have low numbers. If exhaust is hanging open he will have an erratic vacuum gauge. Compression and vacuum gauge are handy diagnostic tools. Start with the basics. I also agree 4.56 to 5.13 ratio wouldnt hurt. But the ratio would hurt his bottom rpm more than top.
