I went from 3.42's to 3.73's and I gained mileage on my RCSB with 5.3 and 275/45/20's because the truck had to downshift less on the highway and had more take off in the city. So if I had to guess you would actually lose mpg's if you swapped to 3.23's.

 

id go with a shorter tire too...

but it all depends on how you drive it..

my truck gets up and goes just fine with the 30.5" tires and 3.42s with the 2.47 first gear of the 80E hauling 10,000#..

 

I live in texas haha
now that you mention it the truck does seem to bog from 47-58ish going up a hill when the tq converter locks up and goes from 1100rpms to 1400rpm maybe I need more gear? Once it gets to 1500 around 60 its fine
around 1700-1800 rpms at 70

Probably once the 210/218 cam goes in over Christmas it will make enough tq to stop the hill bog and just leave the 3.42s

 

+1

Install the cam first, and I honestly think you can benefit from 3.73 gears withouth affecting mileage, heck it could even improve as you'll save some gas in the city.

I went from 3.42 gears and 31.6" tires (stock size on my 4x4) to 4.11 gears & 33" tires and my mileage stayed exactly the same, it didn't moved 1mpg one way or the other.

 

I'm running 3.73's with 275/55/R20's.

My mileage went up after a cam and head swap from about 16.5 to 19ish interstate.

I think going go a lower gear you're going to hurt yourself more than help, because you'll be that much farther out of the powerband. I think what happened with my cam/head swap is I opened up the powerband and I'm now further into it while going down the highway.

 

On long highway trips, the transmission will slip out of the torque converter lock up mode back into 4th gear, I think. Example going 75 1850ish rpms, at random times putting my foot in to it with out making it down shift will cause it to go into "4th gear" 75 2000+ rpms for 1-4 miles, down hill, up hill........Any idea that lead to the rear end or is this a transmission issue?

Kinda off topic of the gear thing....

Yall are making me want 3.73s now I guess I could try try them out and if I dont like them put the 3.42s back in.

 

Careful there you may become addicted to power.

See, I only wanted a little more so I installed a cam... 2-3 years later I've installed gears, headers, beefed tranny, tune, even a supercharger

The best (or worst) part? I don't see the end of the tunnel as the "need" of a larger engine has crossed my mind

 

Will the 3.73 need to be adjusted by the tuner for speedo gauge and transmission? or install and go? I know the hand helds have an option for it but I don't have one haha dynooo tuneee

Will the 3.73s be harder on the transmission?

 

jiar577 do you have dyno #s before and after the super charger. mainly the cam N/A you seem to have the same set up besides larger tires

 

The tune will need to be adjusted for the gear change for shift point and speedo correction.

And if anything the 3.73’s will pull some strain off the other components in the driveline by the way of additional mechanical advantage.