I can vouch for the NP A833. I'm using a 3.42 rear and when I go from 1:1 3rd into .73 4th it almost seems like the engine shut off. I cruise 70 no problem (and when I get off these 45-55MPH roads, then I reckon 80-90 will be breeze too).

http://www.chuckthetruck.homestead.com/page12.html