Just did a family trip from FL to Rutherfordton, NC with appox. 800lbs payload between passengers,dog,toys,luggage, winch, emerg equip, powerwheels jeep and filled coolers with a big horn 3.92 etorque and was impressed with hand calculated MPG heading there particularly. Did it TFL truck style. Have smaller of 2 tanks and could have gone about 450-470 miles without stopping it looked like. low fuel light hadn't come on by 395.5 miles.
Heading North uphill to about 1000ft overall destination elevation over nearly 400miles on 1 tank. (all our bladders could hold!) First 395.5miles recorded 18.3 I was super conservative and kept it speed limit mostly, maybe 5 over at times. always 75 and under. Didn't record til return trip, which averaged slightly higher speeds and recorded 19.03 for first 295 miles and 17.6 for remainder of trip. Not ideal conditions on return trip. We were one of the quicker vehicles heading south that afternoon tho.
Not bad at all, basically what I recorded when empty on flat road with some wind is what we got going slightly uphill with some weight added.. Give or take 10%. I suspect the gains from the downhill swoops/hilly highways gave more savings than the slight struggle the 3.92 had going uphill. I didnt see it drop below 11mpg current on the steepest even with downshift to 7th. then seen 99 on downhill often. (averaging higher than a flat road would yield even tho its going uphill gradually)
I suspect that this winch adding 1/2" sag on front ground clearance with stock suspension + 800lbs payload brought the truck to much lower ride height, maybe 1 to 1 1/2" lower in the front then when empty. I didnt measure when loaded down, but I can confirm a 1/2" drop on the stationary air dam from the 120 lb winch setup added. 9" clearance currently when empty in driveway.
lower=better for aerodynamics but how much does a relatively decent amount of payload hurt MPG vs some minor aero gains from lowered stance.. Interesting.
