I'm no expert at oil or oil change intervals at all, so I can't really offer any sound advice on it, I just go by what blackstone has told me.
With that being said, if I had a new truck, I'd dump the factory fill after a couple/few thousand miles, and start using more expensive oil, and do like what you said, sample it at 7500 miles, then increase the intervals depending on what the UOA says. But then again, even if you just go by what factory recommemds, I dont think you'll hurt anything. This oil change stuff is just one of my little OCD projects that helps occupy some of my time
Some people who are enjoying the free oil changes swear by it. However, I'm gonna change my own damn oil, heard too many stories of dealerships screwing up this simple task, I.e. not putting oil back in, not changing the filter, and the list goes on. Its a very simple task, and I'd rather spend an hour in my driveway doing it, so I know exactly what went in and how much, and I know it was done right. Not to mention, I hate waiting in lines to have my oil changed, and I don't have 2 hours to kill during the week days, where I can drive out of my way, using gas, to go sit and wait at a dealership to have an oil change done, and to just hope they did it right