Differential gear ratio questions

[Magic1]

My 82 Sierra 4x4 is running a 350/th350 with 35 inch tires, 3.08 gears, an open front diff and a locker in the rear. The spider gears were shot in the rear end and to save money I installed a spartan locker which I hate. I'm going to replace the differentials with limited slip front and rear and regear the truck. I won't say it's terrible at takeoff and power now but it could certainly be better. The question I've got is what are a lot of you guys running as your gear ratio with the same tire size/transmission that I have? I've looked at several gear calculator charts and they all show for a broad range of power and mileage to go between 4.10 up to 4.88 for that particular tire size. That seems like quite a jump to me but I'm not sure. I wanna do it right the first time. Just looking for some opinions from those that are running a similar setup.

[Captkaos]

I think I would go with 4.56 or 4.10 if you don't have overdrive.

[Magic1]

I appreciate your response. I talked to a Drivetrain-Differential shop yesterday and they advised me to go with the 4.56. Said they do a lot of them.

[Irish_Alley]

4.56 and 35s you will be screaming trying to keep up with traffic with no od. i had 4.10 with 38s and no od wish i had 3.73. now if you mud yeah you might miss it but thats what 4low is for

[pholliday1]

4.56 is going to make your truck seem a lot quicker in the zero to 55 speed slot. It's a good choice.

[zieg85]

I have a 4.56 in my Yellow extended cab.  I dislike (HATE) it.  Even 50 mph the engine is screaming.  If you never had to go on the highway, probably be ok. If you were running 38's or 44's, a 4.56 would be a good gear.  My $.02

[Irish_Alley]

even in my 91 i have 4.10 and only 29s i think if not smaller. with od im around 2k just going 60. might not be too bad in a gas motor but im losing my mpgs with the cummins.
with 4.56 and 35s you'll be at 3k going 65 and at 55 youll be close to 2500

[pholliday1]

Zieg what size tire are you running with those 56's.

[zieg85]

Zieg what size tire are you running with those 56's.

LT265/75R16

[pholliday1]

Yea I see what you mean 4.56 gear is in the basement for that tire size.

[Magic1]

Wonder how much difference I would be able to tell in going up to a 3.73? With it being so much I wanna do it right the first time and have no regrets but I also don't want to spend the money and not be able to tell much of a difference. Seems like now I'm running around 2200 rpms at 70 or so with the 3.08s. I don't want it to be screaming on the highway but I don't drive it at 70 all that often either. Just want to find a good balance. Also I built the truck for all around use; hunting, hauling trash, getting to work in bad weather. I don't intend on mudding it but rather have something that'll get me there and back if I have to get in some slop.

[ehjorten]

I have 4.10s on my '91 with 35s, but I have OD.  I can fly down the highway with ease.  At 75 I am only turning about 2,100.  For you, without overdrive, the same effect would be close to what you have now.  If you went with 3.73s you would be turning about 600 RPM more and in my opinion, wouldn't be too bad if you driving on the highway fairly often.  I turn about 2,900 in my '69 Chevelle going 75 and it is more than comfortable doing that.

In my '77 I also have 4.10s, but without overdrive and with 33s.  In that I am turning about 3,100 to go 75 and it is just too much to drive that fast on the highway for long periods.  It is loud and it is fatiguing!  Around town it is just fine!

[Magic1]

The more I think about it the more I'm leaning towards 3.73. I think anything lower would be a waste of money and the 4.56 would be too low without od. Jury's out on the 4.10, may like it better but I think the 3.73 would probably work the best for what I use it for

[Gusgusa1]

4.91 that's what I have. She jumps pretty good but revs ( 3000)  at highway speed. 33" tires.

[rich weyand]

I'm running 3.73 with 31s on a K truck.  Mostly around town, but the occasional 200-300 mile run and back.  I think it's about perfect.  2500 rpm at 60, give or take.  So 4.10 would be my bet.