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2005 Silverado 1500 Z71
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Discussion Starter · #1 ·
I've got an '05 Silverado 1500 Z71. Here are some other details prior to asking my question:
  • 5.3 has an upgraded cam, headers, true duals, and an upgraded intake
  • Tires are 1" wider than original, but at 31" tall, are not taller than stock/original
  • Current differential is 3.42, as verified by a reputable trans shop in town

I'm going to increase the differential for 2 reasons:
  • I do "some" towing, and want more low-end torque: I'm pulling a 6,000 lb camper (fully loaded) several times a year, though not long distances.
  • Increase the initial response out of the hole. NOT for racing, just overall performance

The mechanic who worked on my motor suggests 4.10...but while that would be great for towing / torque, it seems the RPM's might be pretty high when doing freeway driving at 70 / 80 mph...even in OD. I know that I can go 3.73 or 3.90 as well.

Any insight from someone who can speak from experience...as to which gear increase would provide better torque / towing, while not greatly increasing RPM?

THANKS!!!!
 

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Super Moderator
2015 High Country Duramax
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18,721 Posts
4.10 all day long, every day.

It's the best gear ratio for a stock, or close to stock tire setup on these trucks.

At 70mph you'll be around 2100rpm, which isn't a problem at all. My 01 had 4.10 in it from factory and it was awesome.
 

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Premium Member
2009 5.3l 6l80
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4,058 Posts

This guy did us an awesome favor.. its very accurate. Just click on the first picture and it will take you to an excel sheet where you can plug in your trans, tire size and gear ratio.
 

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Thanks very much. Currently at 70 mph, I'm at about 1,750 RPM with 3.42. Sound about right by comparison?
If it's not towing heavy or pulling a big hill, which might unlock the tc or cause the trans to downshift, at 70mph the torque converter will be locked and trans will be in high gear.

Makes it straight math using the diff ratios to determine new rpm at 70.

(1750 / 3.42 ) x 3.73 = 1910

(1750 / 3.42 ) x 3.90 = 1995

(1750 /3.42 ) x 4.10 = 2100

etc.
 
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