LubeGard Right for 8-3/4 Sure Grip??

Went to the parts store tonight, kinda in a jam, need to change out the diff fluid cause it seems too thin. I had a friend of a friend install the diff and I'm not sure he got the right Gear Oil in it.

I found something called LubeGard "Limited Slip" Additive, but don't know because it doesn't sound like this is for a Sure Grip. Anyone know if it is?

I checked their website, they mention the 8-3/4 but they don't say anything about Sure Grips in it. I just don't think this is the right stuff. Any input is valuable.

Thanks