you nailed it when you said 90% for pulling. For a do-everything truck, the 3. 73s are good. having said that, remember too that the inertial losses in the engine rise as the square of rpm, so you can still, HPCR notwithstanding, benefit from low rpm cruising. Its just that for pulling, the higher rpms are a fuel economy AND pulling power advantage.
Also, a very cool thing to do is get an after market OD that splits the distance between gears. then you have all kinds of choices for rpms and speeds, plus you have an enormous top speed!