You can get a 3.38 gear for the '55-'59 (and up through '64?) half ton rear end, but I'd suspect you'd be feeling slow from starts with that versus slow up top with what you've got. I'd be willing to bet, based on my experience with my '50 half ton 3spd/4.11 and 216, that you aren't actually pulling as many rpms as it sounds like it is at speed.
