Some of you have suggested a free flowing exhaust. One of the details I really enjoy about this truck is how quiet it is, but at the same time I'm sure that the quiet is offered at the expense of a restrictive exhaust. It's definitely on my list of options to increase fuel mileage and, maybe, performance, just a bit.
Others have mentioned a canopy, which is definitely on my mind. I'm keeping a watch out for a used one, but it's got to be in a matching color. If I throw one of those "they're everywhere, they're everywhere" white canopies on board, the "classy truck" status will be completely erased.
I've gone with the aftermarket free flow exhaust and air intake on other trucks and found that I really could not tell any notable improvement for the good. I have built a couple of engines with mid range torque in mind and increased power and torque which then increased mileage when towing. When my 5.7 decides to give up I have a 383 Stroker waiting for me to finish. My Suburban is a 7000 lb vehicle and it takes torque and HP to move it. By the way "nice looking truck"!
I dont think you'll get much benefit with individual fixes, but maybe cumulative results of changes might gain you an extra couple or few MPG. Just because the science is there, it doesn't mean the technology can be bought off the shelf. "Typically" with better economy, you lose performance. Sadly, it may nickel and dime you to death while you're trying to save nickels and dimes.
A new injector fuel rail with a custom flashed computer program.