I recently had my 2020 NX350 F-Sport in for service. My mileage had been 24-27 with mixed driving. Now it's 20-23. We've had an extended Fall season so it's not a change in the weather. I used to get over 30 on the highway and now I get 24 based on the display above the steering wheel. This has been over 10-mile stretches. Tire pressure is 33 psi, and I'm usually driving solo.

Car has just under 19K miles. Any thoughts?

 

It might help if you disclosed what services were performed. Do you have an itemized receipt from the service provider?
Has the lower mileage persisted over several fuel tank refills?

 

I'm assuming you're using the built-in dashboard/computer to give you your MPG.
One thing you also need to consider is the DISTANCE/RATE/TIME that you've traveled for the readings. Each 'trip' you make with your vehicle is factored into the overall MPG that it continually calculates. Each trip has an element of DISTANCE, RATE (i.e. mph) and TIME that must all be calculated and factored into the 'overall' value it comes up with to show you the MPG on the screen.
You probably know you can RESET this value at any time, and then it will start from scratch with the calculation.

So YOU would need to know what (DISTANCE/RATE/TIME) your "24-27" was based upon. IF you could mirror those driving metrics (DISTANCE/RATE/TIME) then you would be able to see a FAIR comparison.

Here's an example:

** For the last 2 months I have driven every weekday from home to work and back, via highway, with no traffic, at approximately the same speed (i.e. 60mph). My MPG was 25.3.
** I had a tune up this weekend, and A,B,C was performed on the vehicle (what user n0v8or asked in previous post).
** I have now driven almost 2 months, same driving habits, same route, same speed, same traffic. My MPG is now 22.1.

So in this example we can clearly see there is a difference in fuel efficiency.