and 235/75-15s?
that would be like 65= 1960 rpm, with the 3.55s.
4.10s would increase that by 15.5% to 2265, still acceptable, IMO.
I get pretty good fuel-economy at 65=2240.
4.10s are like a half a gear. That will really help those wide NV3500 splits, from Third gear and on.
In my 430 hp car...