Don't hold your breath that a new tank will fix it.
My '11 has had 3 nox censors, a def injector and a new tank/pump in the last 25k miles. 13 trips to the dealer so far, and spent a couple days standed in Ky. with it. Truck has 44k on it now.
As far as I can see, most of them are pretty reliable. But the problem trucks are BAD!
Based on my many conversations with customer service, I think they are just waiting for the 50k emmisions warranty to expire.
Mine will be leaving in the spring. Don't see how I can afford the service bills on this POS once the waranty expires. Since GM doesn't seem to care about actually addressing these issues, I assume they won't miss me as a customer.