10 soeed to 13 speed swap... which tranny model?

I dont know model numbers... But if you can find a "single over-drive 13-speed"... Thats what I would put in my own truck... But they can be tricky to find.

If you really want a little more speed and dont pull over weight... And got $$ to burn... Put a higher geared rear end in... You really dont need that 3:52 for only 80k.

Any way you dice it, a tranny... A rear end... Both... Its not going to be cheap, and it will take several years to get your investment back.

If it were me I'd probably leave it alone and back out of it a little... Unless the tranny or rears took a dump and needed replaced.

 

Are you sure about the 255 tires, those are the baby stepdeck tires, rarely seen on a class 8 truck.
You need to see which model 10 speed you have, some have just as high of a gear as the 13,spd, or close enough to not make a difference.

 

I have an RTLO14613B. I have 3.90 rears and tall 24.5. 1,750 rpms is about 70 mph. This is a single over, .87.

1,750 rpm is a little high for a 12.7. I'd prefer about 1,600.

 

Eaton Fuller 13 double-overs usually have 0.86 and 0.73 ratios. From the numbers you've given us, it appears that the transmission you have now also has an 0.73 overdrive, so swapping transmissions would not help you. Because you are limited to your current tire size, your only option for slowing down your RPMs is to go with a lower rear gear. 3.42 would have you running 1600 RPM at 70 MPH and 1700 RPM at 74 MPH.

 

Couple a different final ratio 10 speeds but by your info you are running a .74 final gear. The 13 you want is a RTLO16913 or a RTLO15713. But they both have a final ratio of .73 that 1 percent difference will not make the rpm difference you are wanting. You will never even notice it. All the 13 is gonna do for you is be closer between gears