[spacemanspif]

Everything said above is good info. I think most truck guys use factory F-body fans with good success. I'm not sure any e-fans pull as much as the mech fan but as we all know, cooling systems are overbuilt.

Intakes won't help you gain power or MPG. Factory intake on that truck is one of the best flowing GM had, it beats the LS1 intake and only the LS6 intake beats it above 4500rpm but doesn't have the torque (main reason I haven't put a car intake on my Monte). A port job might help but is probably not worth the effort/price.

Is it just a road truck? Consider lowering it. Use more street friendly tires (if you have knobby ones right now)

A real tune on a dyno will cost you about $400-500 but will get you better gains than an "out of the box" unit

Buy a scangauge/ultragauge

Upper grill block should help a little too especially with how much front end those truck have

edit: 5.3s only came with 4L60E trans. which is good and bad. Good because you have the better OD, bad because you are already using the better trans and getting 17mpg lol.

If it makes you feel any better, my Monte only gets 19mpg and that car is way lighter and (I hope) had better aero...so you aren't doing so bad lol.