Just checking in for 2021! Since discovering EcoModder, my best modification to date is still currently; Switching from a 2002 Honda CR-V (AWD automatic) to a 2015 Mazda CX-5 (2WD manual).
The weight, engine size, and hp/tq ratings are very similar, but the Mazda uses plastic molding underneath for better aerodynamics and Atkinson cycle (I think?) engine management.
Both vehicles got better mpgs when I slowed down to 61-65mph on my commute.
Of course, working from home because of covid has made a significant impact on mpgs also, but I'm not sure that counts
So I don't have much to contribute, but I usually stop in to see anything new and exciting since my commute is 105 miles round trip, five days a week.