What rpm at 65mph ???

If the price is good and its in great shape you can change the gearsets to whatever you want. Guys change them all the time. Most rearend shops will take them in a trade. 3.70’s and 3.90’s are still wanted by lots of guys.
That is what the math is for.

 

Not sure but sounds “heavy spec” 44,000lbs. Maybe?

 

That would be a good setup out west

 

I got a 13 speed and 3.25 rears and the 13 speed helps carry momentum up the mountains better than most but once momentum runs out and its time to start pulling the hill , would love to have a little bit shorter gears.

But at the same time in my truck u could run out the top gear down some of these straightaways and hit triple digits fairly easy without ever touching 2000 rpm. Atleast thats what my buddy told me

 

My T-680 is the same except I have 3:36 axle ratio. I know at 80mph it’s at 1,600 rpms. 65 mph it’s probably 1,400 -1,450.

Loaded at or near 80k running mountains I get about 6mpg..on flat ground 7+.
Light loads around 8mpg.
Empty pulling a reefer I can get 10 mpg or darn close to it..but that requires me to drive in a way I don’t like

If you do buy it get the valves adjusted.. I recently got mine done and noticed a big difference in fuel mileage.

 

I just wanted to add.. with my 18 speed I can’t even use 18th until 62 preferably 65 mph.

if you only plan on running 60-65 mph you may not like the 18..