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Discussion Starter · #1 ·
Hey guys I'm in the process of changing my gears in my 99 gmc. It's a 99 gmc sierra 1500 base model. It had a 4.3 In it when I got it. I'm wanting to go to 3.73 to 4.10 or 4.56. My question is exactly what gears do I need.ive found many different gm ones like 7.25" or 8". How do I determine which gears I need front and back?
 

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2wd or 4wd
auto or 5spd
what size tires do you want to run
since 99 was a cross over year,what body style do you have,88-98 or 99-07
 

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5.13's
 

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Holy shit bro! 4.3 running 38s? I don't Care How low of a gear you have it just won't be right. Save money and do a 6.0 swap first or even a 5.3
 

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Discussion Starter · #9 ·
And no one still hasn't answered my question. I didn't ask what gears to go with, my question was how do i determine what gears I need. Like what axle length I have. I need to know were I can look on my truck to get the correct gears for the front and ones for the back. I hope that makes sense.
 

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pretty sure 8.25" ring gear was standard on all 1/2 ton trucks regardless of motor configuration
 

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The truck HAD a 4.3 in it when I bought it. I put a 6.0 in it last summer.
Oh shit didn't read see that in your original post.
 

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Discussion Starter · #13 ·
pretty sure 8.25" ring gear was standard on all 1/2 ton trucks regardless of motor configuration
That's what I need to know! I'm looking at the gears on 4wheelparts. So I would need the 8.25" IFS gears and the same "8.25 for the rear? Thanks guys
 

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8.25" front and 8.5 rear. Do they not have a vehicle spec input to produce search results? Or in the description of said parts?
 

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You can also check the Glove box for the RPO codes and find out that way
 

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the rear is actually a 8.6 BUT with a 6L and 38+ tires its not going to last long unless you baby it onroad,and I mean baby
and if you plan on offroading it the front diff will hate you esp with 5.13's

read up on 14bsf and 9.25inch swaps and think wisely before you go blowing money on the stock diffs
 
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