Gears & Axles - Which Posi-Trac Additive?

My SS has around 28k miles on it, so I thought about changing the rear end fluid. I went to Auto Zone, just to check their price on Mobil 1, 6.99, and anyway saw the Trans-X Posi Trac Additive for 3.99. I haven't visited my local GM dealer yet to see their price on the GM additive, but was wondering what the reviews were on this stuff, and which one I should get. By the way, this is a good time to change this fluid, correct, or am I changing it too early? Thanks!!!

Dont use synthetic gear lubricant. Synthetic will cause the clutches in a limited slip to burn up. For the posi additive, just get it from the dealer, its only $7 or $8.

Dont use synthetic gear lubricant. Synthetic will cause the clutches in a limited slip to burn up. For the posi additive, just get it from the dealer, its only $7 or $8.

There aren't any clutch packs in a torsen.

A Trac-Lok like the Mustang uses has those clutch packs that wear out.

Would that Trans X stuff be okay, or should I go to the dealer? I have the regular GM Limited Slip, no SLP options for me:(

I don't know if you absolutely need the additive with the Torsen unit, but I would use the GM Limited Slip Additive.

I have an Auburn rear end, so I am going to run a non-synthetic, correct? Will Mobil 1 80w-90 be okay? I talked to the guys at Autozone, and they said the Trans-X stuff was the same stuff that the dealer has...if you believe them.

On the front it says just "Mobil" 80w-90 heavy duty. Here is a link to the product:
http://www.mobil.com/USA-English/Lubes/PDS/GLXXE2CVLMOMobilubeHD_LS80W-90.asp
it is in a black jug. The additive on the front says it is approved for GM Limited Slips that need the GM Additive as it gives the part number for the actual GM Additive you would buy at the dealership.

I think Mobil is synthetic. I was told to use the GM additive only.