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what rpm do you like to run at your freeway cruising speed? gear it to that.
the Yukon master install kits are really nice for doing gears
 

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Bobs 7.3
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4.30s will put you right where the stock powerband and power would be when running 37s or 38s. 4.56s will up the rpm a bit on the highway but give you a little more at take off. I run 37s with my 3.73s and love the highway running at 17mpg and when towing I just lock out the od and at 65mph it tachs at 2100rpm and purrs right along. When using od at 65 I tach at 1700 and if not in the hills ill get 17mpg in hills I lock out od and let it sing.
 

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7.3_KURT
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4.30s will put you right where the stock powerband and power would be when running 37s or 38s. 4.56s will up the rpm a bit on the highway but give you a little more at take off. I run 37s with my 3.73s and love the highway running at 17mpg and when towing I just lock out the od and at 65mph it tachs at 2100rpm and purrs right along. When using od at 65 I tach at 1700 and if not in the hills ill get 17mpg in hills I lock out od and let it sing.
same here 3.73 with a zf6 and 37s i get about 17 if i go long distance but for the most part 15.5 sometime 16 just driving to work and back. when i tow i get about 15 . but im only towing a jeep. honestly if i were to put gears id go with 4.10s these trucks have to power to pull 38s
 

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I would get the Yukon gears 456. I have had those for a few years with a stock trans and cooler with abts chip as well. I would suggest getting a bigger trans cooler because mine gets hot but that's really getting on it in the sand dunes but going down the express way at 70-75 it runs about 1800 rpm if I remember right. But I love the gears I have. Way more power and I have 37s on it
 

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With the majority of the others. 1st truck was on 37's witha tuner and JWVB and with 3.73's it had no problem whatsoever with 37's and got high 17's on the highway at 70-75. Current is 3.73 with 35's and i actually miss the first setup as i average 14.5-15 now. From a stop first one was quick , i didn't tow however and dont quite get the big lift , heavy tow idea either. Stock TS tunes ? maybe the shifting needs refinement via custom tuning.
 

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Bye-Bye 6.0, Hello 7.3!
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I've hammered on this to the point of buildings spread sheet to run various scenarios until I got what I wanted. What I wanted was 2000-2100rpm at 55mph in 3rd gear for towing my 30' 11,500lb 5th wheel travel trailer. I'm installing an '05 axle swap and was weighing my options between 3.31, 3.55, 3.73, and 4.10 gear ratios. Initially, I considered 3.31 and 3.55 viable, because with both were manageable with the torque of the 7.3, but a 6" lift landed in my lap. The lift was a game changer, no possibility of a 32-33" tire, and no funds for a Gear Vendor underdrive, I was back to 3.73 or 4.10, it was just a matter of locating the axles. And last week I bought a set of clean low miles 3.73 axles from a rollover, so I'm looking at tires with a minimum measured height of 35", probably 285/75-18s 305/70-18s or 315/70-18s, unless I go with a 36x12.50-18. While 37" tires topically only measure 36" and change, in a 12.50 they are harder to come by with a good load index, and 13.50 is too wide for my wheels.

Point being, you need to know what your truck is going to be used for and set it up accordingly. I agree that 4.10 gears with 37-38" tires are an excellent combo, unless you're constantly towing, at which point 4.30 or 4.56 gears would be easier on the engine and transmission. Just don't gear it like the F-550 service truck I used to run, 4.88 gears with 225/75-19.5s, sure it weighed 23k without a trailer, but [email protected] sucked for 2 hours at a crack.
 
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