31.8 m.p.g. is excellent
If you actually get that. Keep in mind that is likely highway only mileage at 60 m.p.h. Diesel is more expensive than gasoline.
I can tell you though that Ram beefed up their gears, bearings, seals, and thrust washers in their trucks after Toyota was rated best for durability after FCA acquired Chrysler.
I don't know about GM.
An aluminum Ford with an Eco-Boost V6 is also very good on fuel consumption.
It seems lately GM is advertising their magnetic ride control's ability to adjust ten thousand times per second. What? Oh, the computer control module can send that much data, but seriously, one calibration per second, or even less should suffice, and I bet that's all the shock valving and solenoids can react to.
My last truck was a loaded '92 GMC Bahama blue Siera SLE 5 passenger short box.
Very nice comfortable truck, 350 throttle body fuel injection, 4 speed automatic.
Back then Twenty two bucks filled it up from a quarter tank (25 Gals.), and it averaged 20 m.pg. highway at 60-65 m.p.h. I had a tonneau coven on it, which no doubt helped.
Drove it from here to Atlanta Ga. once, and my only complaint were the bucket seats thigh support on the outside edges. Too soft for longer trips. By the time we got to Kentucky, it was time to stop, walk and stretch. Power seats may have helped, but I don't think they were offered then. I didn't order it, it came from the GM plant executive pool lot with 3,000 miles on it.
$15 grand total price. I added a rear bumper in chrome ( yes, they were an option then) from Truck Stuff, the tonnaeu, and a bed liner for an extra $700 or so.