Not a surprise. With compression (or boost), always comes a requirement for higher octane, to avoid pre-detonation.
But even the old 5.7L "recommends" mid-grade. I don't remember the cutoff, whether it's 89 or 91, as most of our stations just have one or the other, so I always just select the middle grade. But either way, Ram doesn't recommend regular 87 octane in the 5.7L. The difference is that the 5.7L will still run fine on 87 octane, but the manual states the ECM will adjust around it, and performance will not be "optimal". This likely means adjusting timing according to knock sensor, but not my area of expertise to really know.
Most of our stations here are 87 regular, 93 premium, and then one in-between, whether that be 89 or 91. A few stations (Wawa & Sunoco) have 4 grades, but you end up paying across the board for that, as inventorying 4 costs them more than inventorying 3 grades. So if running the HO, you might end up buying 93 Premium, at stations only stocking 87/89/93.
edit: According to Google, Ram 5.7L "requires" 89 octane. I'm pretty sure the paper manual sitting in my glove box says 'recommends". Either way, not buying regular 87, for either.