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Discussion Starter · #1 ·
Is there a way, without tearing into the diff, to tell what gearing I am running, either 3.73's or 4.10's?

I read in a magazine that our trucks will run, at 75 mph, at 2300 rpms if 4.10's, and 2100 rpms with 3.73's.

my rpms run in between the two, and since i cant even trust my freekin gas gauge, i don't trust ANY guages
 

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I can almost guarantee you have 3.73 gears in your truck rich...
But, look in your glove box...there's an RPO tag in there (bunch of codes on a white tag) Look for a GT4 or GT5....GT4 = 3.73 GT5 = 4.10
 

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The only factory gearing for a DMax is 3.73. If your truck hasn't had the gearing changed aftermarket - it's 3.73.
 

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also tire size can change the rpms.

Jim
 

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Something that you can do is jack the rear of the truck up put a narrow peice of tape or a magic marker line on the top of the side of the tire(12 oclock postion) put another peice of narrow tape or magic marker line on the driveshaft,spin the tire buy hand one complete turn and count how many times the driveshaft goes around while spinning the tire. example 3 3/4 turns the driveshaft went around = 3.73,a hair over 4 turns = 4.10,4 1/2 turn on the shaft = 4.56 and so on.
 

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Discussion Starter · #7 ·
have stock size tires, and no tune, so i was just wondering. wasn't 410's an option though?
 

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nope, not with the duramax. You can get it with the 8.1, IIRC.
 

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4:10's are an option on the 04's..IIRCO

maybe the 05's...thats why they changed the GVWR on the newer to being higher than the older
 

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03 has 3.73's.
 

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If it has a DuraMax and they haven't been changed then they are 3.73.

3.73 has been the only rear axle ratio available in a 2500HD or 3500 with a DuraMax.
 
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