Just got back from 1500 mile trip. Using 89 got 1+ more MPG than 87. Was running 70-75 MPH all the time. Same roads, no load. Normally when just around town and to work I've used 87, but might go with the 89 for summer use.
2019 Dodge Charger SXT 3.6/auto
2018 RAM 1500 2wd 3.6/auto 8 speed
"Life's hard, it's harder if your stupid."
How would you know?