03 f350 with nv4500 revving out at 70mph
 

i swapped my 03 f350 from a 6.0 to a 12v with an nv4500 trans with an np241 xfer case and the truck wont go more than 70 mph without almost red lining. not sure what the gears are in the rear but what ratio would you suggest for the axles? 3.55?? its got a dana 60 front and a sterling 10.5 rear. i tow with the truck but want to be able to go on the highway and not rev it out!!

thanks in advance guys.

Have you upgraded the governor spring? That alone will give you more revs and fuel in the top end, and much cheaper that gears. IMO, at least try it first. You don't have to use all those revs if you don't want to ;)

Most 6.0L trucks had 3.73, but could be 4.10 or even 4.30 (tow-boss?).

Factory 12v trucks are most commonly given 3.55 ratio. You can get 3.55 for your axles, even used ones if you wanted, from 97-older Fords. You may even be able to do 3.31 for extra highway legs. This ratios showed up with the newer 6.7L diesel Fords.

I haven't upgraded the spring. I'll look into that but I also want better highway mileage too so ill probably get different gears. Thanks for your input!