Not to toot my own horn, but I GRENADED my 2012 F150 rear smoking the rears with the locker set to kill mode. Use in a straight line with caution is my advice.
You are correct. I re-read the email from when I received my tune and it aligns with that. 91 is recommended, but in a pinch (or a few), I'd feel more than comfortable with 87. If its more long term, like our current gas situation, ill begrudgingly return to stock.
I'm suprised that nobody mentioned OZ Tuning. My mileage is down a little (hard to gauge with winter blend fuel and remote starts in the am), but im tickled pink with the power this truck makes. And the trans shifts the way it should have from the factory. Not to mention, 1 tune covers 87-93-E30.