I put Castrol Syntorq LT 75w85 GL-4 rated in mine a few weeks ago. So far it shifts great! But I didn't have any problems before either. I got tired of looking for & reading bad things about other oil. From all I reseached, It sounds like the best. The only down side is it's $$$! Online is the cheapest way to go. I would have bought it online but needed it that day. I ended up buying it at a local GM shop that had it in stock.
Castrol Syntorq LT is available in quart bottles from Dodge dealers (p/n 4874459) and GM dealers (p/n 12346190).