I have a set of 4.10 gears from my 7.5" rear for sale. This would increase your rate of acceleration and give it more "pep" in the low end. However you will turn slightly higher RPM's at highway speed.
A low buck swap would be to purchase a set of gears and swap them yourself. Are you comfortable with opening up that differential housing? Is your's LS?
An even lower buck swap would be to trade me a bit of Tijuana's finest product for the gears!
I'm running 4.10s with my 31s and a tired old 2.3 and seems just about right for me. Keeps me comfortably cruising around 80 on the highway. If I only did 65 though I'd probly want 4.56s. The nice thing about 4.10s is you can find TONS of stock ford RBV axles that already have them in it and just swap in the axle instead of having to have gears setup.