You could throw some higher gears in your rear-end.
Im not sure what year truck you have, etc., but I know mine (51 GMC 1/2 ton) came with 4.11's.
My moms 53 chev also has 411's I think. 55 is pushing it with that truck!
With that being said, you can put some higher gears in your rear end, and achieve those speeds. In the January? Classic trucks, they had an article on this same subject.
Hope this helps,
Dallas
