rancherlee

Back from me trip and here is the Snapshot of my trip.
12' Scab 4x4 with 3.55 open diff
And the Actual HAND CALCULATED came in higher for the hole trip a 20.8 mpg so the Trip computer actually undershot by a few tenths!
First off this was in the state of Wisconsin where the the speed limit never exceeds 65mph even on the Interstate so that helped a bit by keeping me to around 70mph

First day, ~500 miles @ ~70mph and absolutely no wind had me at 21.9mpg when I pulled into the Hotel lot. The next 150 miles was nothing but driving around town from tourist trap to tourist trap, getting stuck in bumper to bumper road construction aided traffic , and making several wrong turns which drug the tank average quickly down to 19.2 where I fueled it up a "0 miles to empty" and the hand calculated came out to 19.9mpg (658miles/33.0 gallons). That is the farthest my trip computer has ever been off, usually only .1-.2 high or low. heading back home we took all back country 2 lane roads running ~60mph where I THOUGHT I should really knock down good MPG but a stiff 20-25mph cross/head wind held me to 20.9 on the computer, and I'm sure slowing down for a small town every 10-15 miles didn't help either where I seemed to catch the SINGLE stoplight RED every time. The last day the wind switched around and I had a nice 10-15mph tail wind that kept every "bar" on the gauge above the Average mark and pulled in the driveway with a 21.7mpg average for the return trip. Overall 20.8mpg FAR exceeded my expectations from the truck, I would have been happy with the window sticker "19mpg" and I just about got 2mpg better I will add that I had a cheap homemade 1/2 plywood tonneau cover painted black so I could use the box for secure storage but I don't know if that helped mileage at all.

KKMC

Thank you for your update. Cross winds DO mess things up, for sure. That is good mileage, considering the driving you did.
As a matter of comparison, I do not have a tonneau cover, makeshift or otherwise, but I have considered one.

My truck calcs vs hand calcs are within 0.3 mpg, which seems consistent with your norms.

HerbyJr

I'll try to post some photos like others have done, but I probably get only around 17 mixed driving, with my 2011, 5.0 screw with 3.55s. That's when I baby it!