FYI - if you apply an RUC or GUC to a ticket, it will foul up your receipt in the "MyDelta" section of the website and app, at least from a reimbursement perspective. If you even are lucky enough to retain all legs of the flight on the receipt, it will show the payment type as an e-credit rather than your credit card. The original receipt shows as a line item in your receipts on the website/app, but clicking the link downloads an empty receipt or shows an error.

I would be sure to save your email receipt, or go in and download your receipt immediately after purchase and before trying to apply the RUC or GUC. I am not sure if the same thing happens if you upgrade with miles or pay to upgrade on or before check in, but I suspect it might.