Auburn "Pro" Series? That's close to "tro". They offer an HP series, Pro series, Race series, and ECTED Max Locker, that's it.
Copy clipped from Auburn's website/FAQ page:
Q23. What kind of oil should be used with an Auburn limited-slip differential/ Auburn ECTED Max differential?
A23. Non-synthetic 80w90 GL-5 oil treated with Auburn Gear friction additive, part #504102 (also known as a friction modifier). See Catalog page 32. Three (3) ounces of additive will treat one quart of oil. GM or Ford limited-slip additive may be used. We do not recommend synthetic oil. Auburn limited-slip additive is packed in every box with the differential.