Rear differential/rear end oil
You can use any SAE 75W-90 Synthetic Axle Lubricant that meets GM Specification 9986115 which is basically API GL-5, Mobil-1 75W-90 is fine. No additives
just about any gear oil will work good 75w-90 it doesnt have to be synthetic.
My front diff didn't like regular gear oil (chatter when backing up). I switched to Lucas 75W-90 synthetic and it was nice and smooth.
i use lucas or at truck stops they have oil call power punch that has always worked good for me
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