PUZZLER!!! My new motors a dog! what did I miss?

Well, he got Smith Bros pushrods, so presumably they were measured for the new Hughes rockers, but perhaps the preload is adjusted too deep in the lifters. If the lifters were holding the valves open, I would expect it to break up a bit; they won't likely hold all valves open evenly. OP, is this what is happening when it quits above 4500 RPM?