I think that the benefit to a tune should not be based solely on better mpg. If you plan on trading in your truck every 2 years then prob not worth messing with. If you plan on running your truck out for the long term then heck yes get one.
Getting rid of smog inefficiency with a tune is guaranteed to get you a bit better mpg. Thats what the tune does plus readjusts the programming to now run as if it is running without smog/egr.
I dont know the additional mpg benefit of the 40hp hot tune I put in my 1500. However I did put the same thing in my wife's stock 2016 GC. We do a 100 mile run to the coast on a windy hilly road frequently. She now gets 33 mpg there and back last time we did it. About 3 mpg increase. So that works out to about a cent a mile she saves on fuel with a 700 dollar tune. So how long for the tune to pay for its self based on fuel savings alone? How many cents are there in 750 dollars?!