2017 5.3L...3.42 to 3.73 swap for towing?

BoilerUP · October 30, 2018

2017 Silverado 1500 CCSB 4x4, 5.3L/3.42. Truck is on stock 17" wheels/all season tires and is my daily driver, getting roughly 14k/year put on it.

We have a 32', ~6500lb travel trailer and the truck does just fine with it on the hills of I-65 south of Louisville...but the wife and I are wanting to branch out more in the coming years so we'll probably end up doing the 75/40/26 shuffle through the Smokies. As such, I'm wondering if it would be advantageous to swap to 3.73s.

I know that's only one ratio lower, and doing the swap isn't going to give me Max Trailering capability...but I'm curious if anybody here has done such a swap and if so, what their thoughts after the fact. Figure it might help the truck pull better without overly compromising daily drivablility & MPG.

A SRW 3500HD with L5P would check all boxes...but my current truck is paid for

Thanks!

pronstar · October 30, 2018

I considered it, but the small bump in torque multiplication didn’t warrant the cost. Doubtful it’s even noticeable.

If I do make the change, it will be to 4.10 but that may not be great for you, with stock wheels/tires, when not towing.

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Logan Lanfear · October 30, 2018

Alright ill pull out my calculator and get you some RPM numbers, I'm figuring that you'll want to know about 2, 3, 4 and 5th gears since that would keep you at a good speed. This is calculated with a 265/75R17

With your 3.42 running at 65 on the highway in 5th gear you're turning about 2100 RPM.

With a 3.73 at 65 in 5th you're running about 2300 RPM.

4th gear: 3.42 at 65 MPH = 2850 RPM

4th gear: 3.73 at 65 MPH = 3100 RPM

3rd gear: 3.42 at 65 MPH = 3790 RPM

3rd gear: 3.73 at 65 MPH = 4100 RPM

2nd gear: 3.42 at 65 = 5850 RPM

2nd gear: 3.73 at 65 = 6400 RPM

Now obviously you would red line before you hit 65 in second gear with probably both ratios. But you'd get about a 200-300 RPM bump overall at highway cruising speed. Good if you already have it but it might not be worth it if you have to change it.

aseibel · October 30, 2018

There have been a few others asking about gear swaps if you search around.

For what you are proposing, I also don't think its worth the cost. Remember that gearing changes also affect the computer and void your warranty.

BoilerUP · October 30, 2018

Thanks folks...I saw a number of threads with folks discussing a swap from 3.08s to 3.73s...but none from 3.42 to 3.73.

Perhaps there's a reason for that.

pronstar · October 31, 2018

Yeah 3.42 to 3.73 is only an ~8% difference in torque multiplication...really borderline noticeable.

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pewterliftedz · October 31, 2018

You will not gain any advantage going with such a small gear change, you're better off just staying out of 6th gear with the manual mode at highway speeds. Now if you step up to 4.10, you will see a great improvement in torque multiplication. With AFM still active in your truck, you will see a lot more 4 cyl mode while cruising around unloaded, and will still get decent mileage. Do not fear the gear, I ran 4.56s on my 07 5.3 truck with 33" tires, and it completely changed my driving experience.

Edited October 31, 2018 by pewterliftedz

300 Blackout · October 31, 2018

...I ran 4.56s on my 07 5.3 truck with 33" tires, and it completely changed my driving experience.

Thats exactly what I have now in my ‘14 5.3 and its a completely different truck. Better fuel mileage due to AFM being on much more often. With traction control off in 4hi it’s a beast off the line. Best performance upgrade under $2500 IMO.

BigBadSierra · October 31, 2018

I'm pulling the same weight off of my 3.42 and have no issues at all. It doesn't even get that hot over long trips.

pewterliftedz · October 31, 2018

10 hours ago, BigBadSierra said:

I'm pulling the same weight off of my 3.42 and have no issues at all. It doesn't even get that hot over long trips.

With a 5.3? I think his concern is traveling through hilly terrain. Does yours have the 8 speed or 6 speed out of curiosity?

BigBadSierra · November 1, 2018

13 hours ago, pewterliftedz said:

With a 5.3? I think his concern is traveling through hilly terrain. Does yours have the 8 speed or 6 speed out of curiosity?

I have5.3 witha 6 Speed Trans temp all stay in line.

They seem high in these trucks but that seems to be the temp GM wants it given how hot they let them get before the trans cooler starts to work.

I do run full synthetic oil in the engine and GM runs it in the transmission.

Now there is no running things down an passing them towing this much weight. You will also loose speed on big hills.