I just got my 88 F350 Fummins on the road and think the gearing is a bit low. There is some debate between my father (project origionator) and me on what the gearing IS in it and what is the ideal rear ratio.

6bt no mods Gutrag trans either 4.10 or 4.26 gears. 4th tops out about 55mph and 5th at 68mph

I was also thinking about 3.73 or an over gearbox to be mounted where the carrier bearing is

I don't pull often, though I may pull (8k LBS tandem axle enclosed trailer) more frequently soon. I do plan on doing some longer trips (500+ miles & no trailer) with this truck.

What do you guys think?

 

373 are what most guys are going with