I don't think any of those mods will help MPG. In fact, I recommend just pocketing the cash and use that toward gas. To install those mods for other purposes (performance, sound, etc.) is one thing, but to throw $1000 for negligible gains (if any) in fuel economy seems counter intuitive to me. You can buy a lot of gas for the cost of all those mods, so why not just enjoy your 6.2 the way it is? (Also, you already have a "cold air intake" from the factory.)
Some people have claimed to see an increase in MPG from a tonneau cover.