Ramcharger exhaust 2-1/4 duals or single 3"

I have put a few hundred thousand miles on 2wd Ramchargers and have only ever seen regular 18-19mpg highway on my 92 5.2 magnum. For those that are unaware, that is 600miles+ per 35gal tank! If someone is doing that on a tall 4wd, I'm skeptical, but bravo!

For reference, going from the the stock exhaust on my 90 5.9 tbi to 1 5/8 headers and 2.5" duals w\ welded ultraflows with turn downs (no over axle) was worth a bit more than 2MPG. ROI was noticed immediately. Other things i did for MPG was thinner diff fluids (e.g. synthetic and not the 140wt), elec fan on my 93 (magnum viscosity fans sound like planes taking off), 1-2deg more timing (on EFI distributors you can only set initial). Some sort of multi-spark ignition box helped a bit too though i honestly don't recall how much.

before do *anything* that costs with the exhaust, i would try a test to see what there *is* possible to be gained. e.g. no cats, turn down after muffler. If its not immediately noticed ROI, i put it back together as it was and spend cash saved on more gas or towards buying something thats not a 4wd truck.