$13.36 X 24 (I'll take off two fills just for "oh **** I have no money" weeks) = $320.64
So I'd save $320 a year.
Thus, if I find my upgrades for a good price, it'd take me 3 years to have them pay for themselves. And in my situation...I'll have the truck for a few years more than the 3 if you catch my drift. haha. I'm gonna drive the bad boy into the grave.
Just my thoughts though......................
And no the upgrades aren't just for economy. They're to get everything out of the truck that I can. I hate to drive a vehicle that has great potential laying beneath that stock paper air filter. Just my $.02
With the mods you are describing it will take more like 5 years IF you get 3 mpg. I have those mods and got 2. If you are doing the mods for the power then WTG. If you are doing it for the fuel economy.. don't spend the money.