I agree you should change to some kind of lsd at the same time because you'll have to pay someone to set those gears up properly and then pay again sometime in the future. You could consider buying a complete re-built center section or get the components and do it yourself if you feel capable- the difference is about $200 labor. I bought a used center section with 3.55 and detriot tru-trac from a trusted member here who was switching to a nine inch rear. Be aware that these don't come up to often so have your cash ready. Which gear set you go with depends on your amount of highway driving 3.4 and 3.55 are not that different and I would focus on the difference between those and 3.25 which is about 240rpm at 60 mph. Oh and since you have to pull both axles when doing the job you'll have to buy axle seals as well (and check the axle bearings). John
"If you need a new machine and you don't buy it, you pay for it without getting it." -Henry Ford
Last edited by 64.25; 01-21-2013 at 10:32 AM.