3.25 rearends 9 speed Trans Converted to 13 speed. Want to upgrade

That was most likely an 8LL or if it was in a smaller vocational type truck it was a 6613. Which had the round knob with 3 position switch. Ran the first 3 in bottom, all 5 in intermediate and last 3 on top. It was actually a 15 speed with 13 progressive gears. Which is all the big 15’s have as well.


If it was me I’d a bought a truck that was specked for what I was doing. Being honest then 3.25’s on low pro 22 will be close to 3.55 on tall 24’s. Maybe 3.42’s I haven’t done the math I’m just shooting from the hip there. I will also say up to a certain point higher gears on smaller tires will be more efficient than a tall tire with lower gears that has an equal road speed to engine rpm. I think they may pull a tad better too. Horsepower not gear ratio gets you up the hill. So a smaller lighter tire takes less of it to spin it. (Example 3.36 on low pro 22.5 is close to 3.70 on tall 24.5 at same speed the engine RPM is crazy close) Much past 3.08 and they get pretty hard to get rolling with any tire size. That said I’ll keep my tall 24’s at less revolutions per mile i don’t believe they heat as bad. I pulled a trailer with a lowered jail and tail with the 255/70 22.5’s and that first summer was a battle with tires. At first I thought it was cheap tires from Wilson new #### never comes with top of the line stuff. New tires same size wasn’t helping much. So I put a set of hard used 24 low pros wheels and all off my hopper. Problem ceased but I had a new problem I was 13.7 inches. Had to watch my tail like a hawk. Gotta give to get never a perfect solution and you can spend thousands justifying it on paper to gain nothing