The result was disappointing: 25.3 MPG.
Yeah, but what a road trip test! Nothing to sneeze at with a 16-cpm average at 70-mph. I calc 15-cpm at 58-mph (all at $4/gl). You "earned" the shorter drive times is another way to look at it.
And anything above 95F is hard on a non-aero vehicle, IMO, as the big cooling system on these TD's start to have to work (My assigned 367 Pete starts to suffer at this point in the 95F/60% humidity days here in South Texas [which is different than North Texas]). I read that higher temps are helpful for mpg in general, but there is -- so far as I can tell -- a cut-off or trade-off that occurs at some point.
On my dead stock pickup seeing 22/23-mpg at 68-mph/1,900-rpm is a "norm" for this time of year, so your 15% plus improvement over mine is nothing to sneeze at . . you already know that if you'd kept it at no more than 65-mph that the numbers would have been even better.
Thus, I also find it useful to look at
average mph over extended distances as this includes all driving plus idle time. It's then a fair way for me to
trip plan and keep any (necessary) cab cooling to reasonable minimums (and a 160F interior temp is unacceptable; etc). This average, plus fuel burn is what informs me more closely no matter whether solo/empty, solo/loaded or either loaded or empty plus towing (any of a variety of trailers).
Here's an example.
With a pickup truck I need to be able to understand -- predict -- my fuel burn via climate, terrain and use.
Then a pickup can come into focus in the ways a car is not ever called upon to do.
Your experience with 3.08 gears has caused me to look closely at the AAM replacement 3.42 set for my stock 3.73 gears as it would, town & country, keep me closer to the sweet spot instead of always being just above it.
As to seeing out of the back, I cannot see out of my topper (glass replaced with wood and some security reinforcement), but the stock DODGE towing mirriors (down) aren't as bad as those FORD towing mirrors would appear to be. I will be trying the full replacement CIPA mirrors on mine at some future point, and am hoping they aren't the elephant ears they appear to be. SCHAFENACKER [sp?] has some that might work for you as an interim compromise. (And I liked that old idea you had of a Pontiac Trans Am rear window louver set).
Look forward to seeing and hearing more.
.