I’ve had 3.08s for about three years now and I am delighted with them. Few people can approach the MPG I get, and the 3.08s are a large part of that performance.
Contrary to popular belief, I tow quite nicely. If it lugs, I down shift to the most efficient gear – fifth. I have pulled heavy loads over the short steep hills of eastern KY and western WV and had no trouble at all. With 10,000 lb of building materials in the bed and trailer I got 15.5 MPG. I have no fear of Sandstone Mountain in WV.
I normal driving I get over 26 MPG on a regular basis in mixed urban/suburban/country road/Interstate driving.
Smokey is dead on about the RPM. With 3.73s and factory rubber 2000 RPM is 69 MPH. With 3.08s and OEM-sized rubber 1650 gives you the same 69 MPH. I run 1700 RPM which is 71 MPH on the slab. 1450 RPM gives me 60 MPH.
Slowing down the engine at a given road speed reduces the engine frictional HP and that is where the MPG gain comes from.
I have a manual transmission and I do fear that the slow-revving setup will destroy an automatic. Maybe Brian or Suncoast or some other respected transmission guru would care to weigh in on the subject. I am not objective about automatics after seventeen years of torment with my old 6.2 Brand G.
I have found the 7.3 to be a real torque monster at low RPM. It accelerates nicely at 800 RPM. I rarely rev over 2000. I’m still on the OEM clutch.
Any regrets? Yeah. I wish I could have found 2.73s for the Sterling 10.25” axle. The ring gear may be of too small an inside diameter to accommodate the differential, but the lack of 2.73 availability may just be a commercial thing. The engine could handle it, I’m sure. I’ve experimented with starting off in 3rd and it seems to do fine. 2.73 gears would push my 71 MPH down to 1500 RPM.
With diesel going for over $3/gallon, I estimate the payback on the mod at about 50,000 miles. A GV overdrive (had one on another truck – the automatic-eating K2500) would cost twice as much (installed) and I don’t care to push more than one overdrive mesh.
I have walked the walk on this setup. I have over 100,000 miles on it with no gearing, clutch, or transmission related trouble.