@indycole....amazing writeup and record of your trials, tribulations, and journeys. Learned a lot.

Gotta get those solar window covers!!
I'll comment on my mpg experience so far on my 2014 LC that is not weighed down except with some temporary Arb drawers, guns and tools.
As for mpg........I just re-geared, Did the 4.88's thing and Arb lockers.
Still have my stock plactic in front and back. Jason is doing a V2 set of bumpers for me also now that
@TonyP has beat the mortal crap out of V1 and been our test pilot.
So, With 4.88's and still running stock 31" tires for a few more weeks, and no appreciable weight load in my truck , I am driving back and forth 3 hours to San Antonio a lot checking a small subdivision I am building. Doing approx 80-85 mph, (the speed limit is 80 on that stretch) and kinda high RPM's till I get taller tires, I am getting 14-15 here in flatland Texas and 11-12 around town. I will be watching to see what the bumper and winch change does to my mpg as I increase drag and weight. I am also adding a 40 gal fuel tank, Tundra long travel front end, & 35 inch tires so I can get my RPM's down to 2000 at 70 mph. I'll be watching to see what each change does to my mpg and basic drivability.
One of my goals with my build is keeping my rig as light as possible. 2nd row seats are removed to use for storage space as you and Tony have done & Aluminum Budbuilt skids under. I am about to use a set of Arb drawers temporarily but consider the construction old tech and unnecessarily heavy.
I have subcontractors I use sometimes that work with various metals and high tech plastics. They are telling me they can duplicate the Arb drawers at half the weight and stronger with no squeaks using plastic that fuses together or aluminum. Since they also do metallurgical testing and various things for Nasa and have access to some unusual materials I am keeping my fingers crossed.

)
Thought I'd comment on the MPG's since my vehicle is evolving now every couple of weeks.
I should add that I have broken my aerodynamics a bit with 2" lift from a BP-51 kit.
cheers,
Jim