ok how about keeping the truck 2wd but add a 4x4 transfer case, electric motor/gen connects to the front output shaft on the transfer case.
2wd would be diesel only,
4wd would connect the electric motor directly to the rear drive shaft for hybrid or re-gen
with the transmission in neutral you would have electric only.
with electric assist and low range when needed you could probably switch to a very high final drive ratio
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