Delvac 1300 is good stuff. I have a gallon in my basement for use in my lawnmower and pressure washer. I've run it in my truck and wife's car during warmer months too. Ran back when I had my 2006 5.9 diesel as well.
I'd run a cheap 15w40 changed once a year. You can get 2 gallons of Supertech for $24, 1 gallon for $13. I bet you could do the whole oil change for $50.
I would like to second using a MB229.5 and/or A40 oil. Try not to concentrate so much on the viscosity, and more on the approvals an oil carries. It is far more telling of how the oil will behave than some numbers that very loosely indicate a viscosity range.
The wheels can easily be swapped over to something more in line with ones tastes. They're not my preference either, but to each their own. The rest of the truck is drool-worthy.
I wonder what's lurking beneath the bonnet... I'd love to see a GMC big block V6 in there.
I used to run 15w40 in my VP 305ci. If I still owned it, it would have either Delo or 1300 in the sump. Not that I have anything against running 0w40 in there, I just have more HDEO stockpiled.
I love the Duratec 2.5, and really any of the MZR based engines. I'd encourage your lady friend to hang on to the car after she gets a new one. Dealer isn't going to give her squat on trade in for it, and it would make a great backup/road trip vehicle if you have the space for it.
I was lucky enough to catch Epica playing a show local to me a number of years back. I think at that time they were touring for their Quantum Enigma album. Simone and the rest did not disappoint. So much so that I bought a T-Shirt (something I rarely do) and wear it often.
I'm going to interject in this heated debate to state I just ran 10k+ on my BMW 328i, N52 engine.
This certainly isn't my norm, all other changes under my ownership have been between 5-6k. Still, I'm not losing any sleep over it. 30+ mile commute, and it sees 7000 rpm at least once a day. Oil...
To me, that is a face not even a mother could love. Absolutely repulsive.
That said, I like hearing from people who love it. I don't see it same as you do, and that's what makes this world go round.