Autozoo has a sale on Valvoline Premium Blue 15w40, this is the diesel engine oil endorsed by Cummins. It's buy 2 get 1 free, so you could stock up on 6 gallons (about a year's worth) for about $52, plus you get 2 AZ rewards points towards $20 off. Or, buy 12 gallons for $84, subtracting $20 rewards bonus. Might be good if you want to stock up on oil or want rewards points at az.
Here's the circular PDF.
http://www.autozone.com/images/in_our_stores/promotions/circular_0212_09.pdf