The TBI motors could be long lived. Swap on some Vortec heads and go to town on mods. I want to say, the later Vortec motors were up on power, but the multi-point injector spiders could be problematic, maybe too problematic for what you are after, hence the suggestion of starting with TBI and building what you are after.
Otherwise, shop the LS motors. Some of the 5.3's lacked AFM, not sure what years. But the 4.8 avoided AFM altogether, so put the 4.8 up on the list. Only thing is... I want to say they did get VVT at some point? Still. Early LS motor is I think what you are most looking for, in terms of simplicity and ruggedness/durability.
BUT
They would all have gotten the 4L60's. Which you might be ok with, or you might think is a mixed bag of worms. They clearly can be rebuilt to last, and some lasted huge miles right out of the box--and some didn't make it to the end of the block. At some point the rest of the truck comes into play, as it's no good to have a great motor in something stuck in park.
The 4.8's in the 1500's stuck with 4L60 (4L65?) while 5.3's and bigger got 6L80/6L90/?, so again, shop the package.