Welcome!
What is your baseline MPG??
Full size trucks are tough. They are heavy and aren't very aerodynamic. There are users on this forum that have gotten some pretty amazing mpg, though I would argue that it is mostly their driving, not the mods to their trucks. They are pulse and gliding, engine off coasting, not speeding, etc, etc. Look here for ideas.
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
Tuners are usually not worth it since the payoff is a very long time in miles and there is no real proof that any tuner actually raises mileage. Plus, is there even a tuner available for your truck?
Pump up those tires too.
I am going to ask, but please don't feel like I am attacking you...why the need for a full size truck??