These are the exact questions I was going to ask.
This summer I drove from Alberta, Canada down to Moab, then over to Yosemite, then up to Whistler, B.C., then back home for a total of 6,000kms. I’ve always towed with 87 octane because gas is expensive in Canada and I honestly didn’t think it would make much of a difference. On that road trip I switched to 91 and I’ll fully raise my hand and say ‘I was wrong for running 87’ because I 100% got better fuel economy as well as performance. Over that entire trip with mixed octane, mountains, and +39˚C temps, I averaged 20L/100km (12MPG).
For context, I have the 3.5L EcoBoost as well, 6-speed transmission, and 3.55s (I plan to install 3.73s but wasn’t able to before that road trip). My trailer is 4,500lbs empty and it was approximately 5,250lbs given I had a full tank of water, full food load-out, and lots of outdoor equipment. I even had 300lbs of fuel and truck parts in the bed of the truck. Oh, and I also had bilateral exhaust manifold gasket failures (haha).