Apparently.
Why is it that you think running in 4th gear will make you get 10mpg? The whole point that everyone else here is saying (and you've chosen to ignore) is that 5th is the WRONG gear with those tires and 4.10's under most conditions on the highway. 4th puts you where you need to be in the power band. You're the one choosing to ignore the FREE advice you ASKED for.
Your truck will cruise until the tank runs dry in 4th on the highway and get better fuel economy than you're getting in 5th, and have more power available at the same time. That you choose to convince yourself that you know better doesn't make you right.
Changing the rockers around (and pretty much every other engine modification except forced air) will let the engine rev higher. It doesn't increase the amount of airflow per cycle, which is what you're looking for. It would actually make the problem worse given you're reluctance to shift properly.