I encountered a similar issue when I bought my Yukon. My "old school" mindset and engine break in, wear in, seating rings, (all the old stuff from my motor building days) was still present and when I called my dealer (like you, my dealer included the first 3 services), he told me they wouldn't change the oil until the gauge read <30%. I was still at 80% and had racked up about 500 miles (maybe). I had to wait about a year and all of the research I could find (opinions vary) said the newer synthetic oils didn't need the same oil change the older ones did. Whether it's BS, or sales tactics, I believed them and figured if they weren't pushing to do services, (which is a revenue stream) they were probably on the level. I wasn't able to get my 3 free oil changes, (it was limited to the first 24 months of ownership) and as I don't put many miles on my truck anymore, I got 1 free one. The mechanics reiterated the synthetic oils don't break down like the older stuff used to and GM recommends 5 K to 7.5 K miles between oil changes. Hours/Time on the motor may differ, but I have pulled my dipstick out a number of times (no pun intended) and verified the oil levels, condition (no glitter or dirt) often and it seems to be holding true.
Like any one of us brought up with the deeply ingrained care for our beloved vehicles, I get the oil changed about once a year, usually when I go to the dealer for a check up or service. It's been about a year since my last oil change, the oil panel still reads 75% +/-, but I'll have them change it next time I bring it in, I put about 3 K miles a year on it. If you're demanding more (high heat, hills, lead footed, etc.) change it when you want. 5000 miles (or hours) seems like a reasonable amount, so it's your rig- and in theory, changing the oil more frequently than others, won't hurt.
I will add (and this may an obvious one) change that cabin air filter about as often too- Just my opinion.