I went from 255/75 MTs to 315/70 ATs and my mileage has stayed about the same, roughly 25 mpg. I drive anywhere from 68 - 72 mph, most of my miles are highway.
Did you calibrate your speedometer? 19-20 honestly seems a bit low if you're doing mostly highway.
If the payload of a 1989 Comanche Metric Ton is a 2200 lbs, I think you would have been fine... ;) (yes I know, coils vs leafs)
In all seriousness, it looks good! It's almost worth the reaction I'm sure you got from the dude loading it up.
I picked this one up when they had a combo deal for a free battery and charger, works fine! Some of the Milwaukee stuff is a bit too expensive for my taste/use.
Not sure if anyone else has done this, but I added two washers on each side to the steering stop bolt in order to stop rubbing on my stock rims + 315/70R17 BFG KO2s. Yeah, you lose a little turning radius... but let's be honest, it wasn't that great to begin with, lol
I went with 315/70R17 KO2s, no rubbing while on the ground (can just fit a finger between sway bar and tire when fully locked), but they might run on full lock while moving, not sure yet. Haven't lifted it or anything.
Folks with Rubicons, Mojaves + Max Tow have the wider axles, which I think...