All adds up. Just left the Ford dealership, comparing the Lariat to a well equipped Elevation trim Canyon.
Basic takeaway is the Ford motor is better, and by a lot. The 2.7 V6 is fantastic, way faster than the GM 2.7 despite similar claimed power and more torque for the I4. By all accounts gets better mileage, too, though how much better is hard to pin down. The GM motor feels very diesel-like, pulls on torque, but without much urgency. Still fine, but not the rocketship that the Ford is.
But the GMC is much more nicely put together, is a nicer place to sit, has a marginally longer box (only by a few inches, but that's the difference between being able to use a bed extender with the RC51 vs the tire at the very back of the tailgate), and looks better to my eyes, at least in black. It feels more like a well-appointed semi-luxury vehicle, as opposed to the Ford's work truck aesthetic. Nothing wrong with work trucks, I think they're super cool, but this is our only vehicle. Also don't like the Lariat pleather upholstery, would rather stick with cloth and nicer seat covers.
In the end, looks like we're going with the GMC. The Ford dealer tried really hard to make something work, and gave up way more in dealer deductions. But the GMC is cheaper to start with, and we're financing a good chunk, so their massive advantage in rate (3.99 vs 5.99) made the deal, even over five years. If Ford was as aggressive with the Ranger rates as they are with the F-150, the deal would have swung the other way...
Still have until Monday to change my mind, though! Have flip-flopped about a hundred times on this one, and the margins were very fine. Calculating for our fuel use against real-world data (Ford advantage), consumables (draw), maintenance (draw), significantly higher insurance for the GMC, etc., the difference came down to a microscopic $648 margin to the Ford over five years, functionally identical considering the variables. I've never been more tortured about making a vehicle purchase choice before...