Rear end question

[Eddieh]

First post here, I'm trying to figure out what gears I have in the rear end. Glove box says GU6, 3.42 but the rear end is stamped GM4... what gives? Also, its a 14 bolt but does have the square sides like others I've seen on this site. Help identifying would be appreciated. Its a 91 k1500 ex cab I bought the truck for my boy. I am planning on doing a 6" Fabtech lift with 305/70R16 tires.

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[polar]

If your glove box says 3.42 you have 3.42 that gm4 is just a casting number

 

[Eddieh]

Thanks, the RPO codes are hard to make out due to wear but I'm pretty sure its says GU6. Im hopping I don't have to swap out the gears to run the 33's.

 

[polar]

Well GU6 is the only one with a U I'm pretty sure.

 

[polar]

I stand corrected. There are 3 with U in them but I doubt you
would have any of the other two

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[Eddieh]

Im pretty sure its a GU6, comparing the 4 and 5 against other legible codes don't look close. Surprised to see such a high gear in a HD rear end.