I had the rear end open on my '05 a few months, (about 10,000 miles) back.
Same rear end as your truck.
I used a house brand from a local inependent shop.
Something or other Synthetic 75-140. It seems to be working perfectly.
Assuming you have an open diff, I suspect you'll be fine.

The guy you talked to mentioned "problems". Did he elaborate?
Leaking?
Nosie?
Bearing failure?
Gear wear?

Thanks.