Two words: Tundra Hybrid.
They’ve flirted with a heavy duty Tundra, they’ve filed a patent on a 4-speed multi-stage hybrid system with a low-range transfer case after it, and it’s well-known that Toyota’s working on a hybrid Tundra.
The powertrain in the Lexus LC 500h and LS 500h is a 4-speed multi-stage hybrid system, and the LS 500h application has an available transfer case (Torsen center diff, and single-speed, though, rather than the part-time 4WD low-range transfer case that a truck would use). As it is, with a V6, it’s got 354 hp, and I think it’d be perfectly adequate for a half-ton Tundra, even with the 1.1 kWh battery that the LC/LS use (more capacity wouldn’t hurt, though).
However, there’s room for improvement, especially in a heavy-duty application, where you’ll be towing. AFAIK, the 8GR-FXS is nothing to write home about in terms of thermal efficiency, and Toyota’s got better engines. How about starting with the A25A-FXS, a 176 hp 2.5 liter with 41% peak thermal efficiency, and joining two of them at the crank, to make a V50A-FXS, at 5.0 liters, 352 hp, and still 41% peak efficiency? (And, add 59 hp to that for what the hybrid system gives you - 411 hp, with full power at very low speeds and CVT smoothness, can fight diesels.)
Then, add more battery - this will help greatly with towing in mountainous terrain (both with power climbing mountains, and with efficiency descending them). The Prius Prime’s battery could probably fit under the truck without too much trouble, and if you give it a plug, there’s tax credits available for the thing (which may also mean that even more battery wouldn’t be a bad idea, up to 16 kWh). Oh, and you could also have an inverter so that the truck could work as a generator, too, on a job site (or, if you’re towing a camper, maybe fully powering the camper off of the truck, when boondocking?)
Upshot is, you get something with a much simpler engine than diesel pickups, far less worries about fuel quality, systems with proven reliability (unlike the proven unreliability of modern diesels), lower maintenance requirements, while still having high fuel efficiency and power everywhere. And, there’s some cases where a plug-in capability could be helpful, too.