what do i have?

Open your glove box and look for the GT# code and tell us what it says.

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thanks, i'll see what i can find tomorrow!

compare your glove box rpo codes to this GM Master RPO Code Listing

ok i had 2 stickers in glove box, 1 is the service parts id with columns of letters and numbers mostly in groups of 3 the other is about camper load stuff... no where do i see at GT code, there is a GTin my serial number but other than that nothing.

Click the link I provided and compare the columns of numbers also known as rpo codes. It will tell you every option your truck has

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It won't be GT. It will be most likely GU6 which is 3.42.

But here are the codes to check anyway. Look for the ones that begin with "G"

GU4= 3.08
GU5= 3.23
GU6= 3.42
GT4= 3.73
GT5= 4.10
G80= LOCKING DIFF

thanks i ran my vin through one of those decoder sights and got all the info except the gear ratio lol
i found ( in those many rows a GU6 and G80 beside it so im good thanks so much for the help. i figured either 3.42 or 3.73, wasnt sure about the locker though, i always thought it was the traction control kicking in and limiting the power till it locked up and got traction...

any special fluid to use in the rear for the locker?

The traction control on these trucks makes them practically useless off road if you get stuck.

My father's 09 literally would not let the wheels spin when I got stuck in snow. I had it in 4 hi and foot to the floor and it would spin the wheels for a split second then cut all engine power so it was just idling. You can't even shut it fully off when you press and hold the button to "disable" stabilitrac and traction control. Only way is to put it in 4 lo or pull the fuse.

As for the oil, no, do not put any additives in there. It just takes regular 75w90 gear oil. You'll likely notice most of the name brand gear oils say limited slip on them. I've used mobile 1 and valvoline in several trucks with the G80 and haven't had any issues. As long as you don't add any more you'll be fine.

thanks a lot!