2015 Sudden Mileage Drop

I drive a 2015 4, purchased new in late 2015, that currently has about 50k miles. Around 4 months ago, I noticed a couple of things:

- A sudden drop of around 6-8 MPG (display). It doesn't seem to be weather dependent. I'm in Texas, the a/c is always running. If anything, it seems like the MPG might be creeping even lower than when first detected. This is based primarily on a very frequent drive I make, about 60 miles, predominantly highway in the country with very little traffic or variability. I always reset the trip computer at the outset. From 2015 until early 2019, I always clocked 50.5 to 51.5. Now it's consistently 43-44. Same conservative, coasting-heavy driving style.

- There's an odd feeling & sound, noticed especially when coasting. It's difficult to describe, but I'd say it's like 'friction' or a very high-freq vibration. This could be imagination, but it seems like the car isn't rolling as freely as it used to. It's subtle.

Dealer has [allegedly] checked for issues twice, and hasn't found anything. They [allegedly] checked alignment & brakes. They drove it and 'couldn't get it to replicate the issue I was having'. I hate that place and am obviously suspicious of their competence and/or honesty, but it still has a service agreement with them (never again), I'm not DIY and don't know where else to go. This is in Austin.

My wife also drives this car and confessed to hitting a curb (or two) around the time that these issues started. We lost one of the plastic trim pieces on the rear wheel well. But again, the dealer checked alignment within a week or two of that incident and said it was still within tolerance.

Tire pressure is checked semi-regularly and stays close to 40psi.

Any thoughts are appreciated.