I remember reading about the Ram 6-speed having a little too much gap between the lower gears. I think the problem lies here, rather than having to do with the rear end gearing, at least to a point. You should look at a chart, showing your transmission ratio in each gear 1-6.
The 5.7 is a proven engine, with lots of power, and very close to the ability of the other late model gas engines.
I wish my Ford had the same transmission ratio in reverse, as it has in first. I guess they build them to fit the average, rather than any one persons situation.
Jerry