Upgrading a 1500 4x4 for travel trailer towing

[Marky Dissod]

Well, I started out with 3.42 and cruising at around 1,750RpM and now just over 1,900. So 4.30 would be 300RpM more at the same speed.
Going to hear those extra RpM through the cab. If I were a kid street racing, maybe, but not now.

Use my calculator, it's more accurate!

3.73, 275/65R18, 70MpH, 4L60's 4th = 1915RpM . . . Makes me miss my Caprice wagon with 3.42 & 235/75R15 . . .
4.10, 275/65R18, 70MpH, 4L60's 4th = 2105RpM . . . Soon as I find a 4.10 rear axle and a 4.10 front diff . . .

4.10, 275/65R18, 70MpH, 6L80's 6th = 2015RpM . . . Schidt. Just convinced myself. If I ever get a GMT900 with a 6L80, 4.10 - and I may never tow anything.
By then I'll be old enough to have suffered just enough hearing loss that I either won't mind or won't notice the extra RpMs through the cab.

 

[swathdiver]

3.73, 275/65R18, 70MpH, 4L60's 4th = 1915RpM . . .

Close but no cigar!

 

[Marky Dissod]

Think I'm using unloaded diameter (32.07") vs rolling diameter (31.125").
Also I think you used 0.696 for 4th, vs 0.7.

So, which calculator are you using? I was using

MOTOR - A Rear Axle Calculator

 

[DaveO9]

Another vote here for 3.73 vs 4.10. Same thinking as others - base it on desired RPM for desired speed in 4th gear. Another consideration, the 6L80 has a much lower 1st gear (about 4:1) than the 4L60e (about 3:1). 4L80e was an even higher 1st at about 2.5:1. So older rigs with 4 speeds, low axle ratio was sometimes needed for starts with heavy loads as well as cruising and climbing, but less of a concern with the newer transmissions.

I started with 3.08 gears and just went to 3.42, based on the two considerations above. But I don't plan to tow near as much. (and there are times I wished I went 3.73) I went the 14-bolt route, too, and all is well so far with the rear end. Not so much for the 3.42 used front I got. My other recent posts are about how it is eating a bearing or similar, and I need to replace it.