It would be nice if GM would just put the DEF fill on the other side if the truck instead of under the hood. I guess they think we are all morons, and would put diesel in a blue-capped spout.
I think the biggest issue is age, as long as it's fresh you should be ok.I have filled twice since I bought the truck with 12k miles. Once right after I bought it, and then again 4k miles later. This time I let it drain down to about 19%, then filled it with 5 gallons. We will see how long that lasts. They only had SuperTech Walmart brand, we will see how that works. I can't see paying more money for the same stuff. I had heard that WalMart buys DEF from Peak. Don't know if that is true or not.