Straight 9 speed

I've drove a direct 10 with a DD13 Cascadia. It had 2.36 axles and pulled like a champ at 80k going east. But it was a 65 mph ex H.O.Wolding truck.

 

So than you must have direct drive trans?
You best option would probably be to turn your 9 speed into a 13.

 

No I mean turn your 9 into a 13 speed.
Should be about one day of labor. If clutch and other doodads are in spec.
With a .73 final drive ratio, I figure your truck would be geared for about 110 mph on the flat roads.

 

Please check the road ranger website.

That will give you the best idea of what an overdrive transmission will give you if you change to 24 5 Tires, get an overdrive transmission Etc.

There's a conversion kit to change a 9-speed to a 13 speed is what @Intothesunset is talking about.

Not all 9 speeds can be converted to a 13. You need to go under your truck and get the transmission numbers end call any Eaton Rebuilder or check with the Eaton website to see if that is possible with your transmission.

You have a newer truck so I would imagine it can be converted, but you still should check to make sure..

 

Overdrive isn't to the dash vs back by chance... Just making sure you are in top gear.

 

Probably better off swapping transmissions. IIRC depending on the transmission model the OD is done in the main box. I think a lot of the aux sections are actually underdrive/direct with regards to the splitter. So with a direct main box putting a 13 speed aux on the back might not do anything at all in regards to higher top speed.

 

You have run out of gears theres nothing more that you can do without major work