A tuner can improve throttle response, adjust the speedo for different size tires & wheels, correctly meter fuel delivery to remove the lean condition tuning of the stock PCM, optimize timing and control spark just to mention a few things. Don't look for any real MPG improvement until you learn to keep your foot out of the throttle after doing the programmer and associated mods. It's hard to do because the truck becomes a lot more fun to drive.
I like the Diablosport programmers and have programmed several of my own MOPARS with them. The canned tunes that come with programmers are lacking in real performance though. I'd suggest you get one that can accommodate custom tunes which are available from several sources online. I tuned my 2007 Ram 1500 MegaCab 5.7L with canned tunes then updated that with a custom tune. It ran a lot better and over the road MPG did improve but just a little bit. The custom tune I got from Hemifever for my 2014 6.4L 2500 Ram was awesome as was the custom tune installed on my 2006 Chrysler 300 SRT8 using Diablosport CRM software and a dyno session where the tech tweaked the program. Both custom tunes were integrated into the vehicle's PCM via a Diablosport programmer. The SRT8 tune was a mind blower.
Couple a freer flowing cold air intake and freer flowing exhaust (sometimes all you need is a better flowing muffler) and the programmer will take advantage of those two mods, working as a system to improve performance.
You won't need an unlocked PCM to tune your truck due to its production year.
