Wheel and tire combo affect the speed, too -- what size are you running? My 3804 with the 216/SM420/4.10 rear gearing could easily cruise at 55-60, dash to 65 on a flat or down hill and now and then could hit 70. But I'm running 7.50 x 17 wheel/tire combo. The 17's are probably like an overdrive. If you're running 15's, you might think about switching to 16's at least. 17's are hard to find.
Doyle -- Have you thought about doing the rear axle 3rd member swap to get the 4.10 gearing? If you aren't really hauling much, its a good upgrade and easy to do.
