Why has my mpg dropped so much? I'm using the same gas, dealers, same driving. on 2010 Hyundai Santa Fe

I have a 2 yr old Hyundai Santa Fe. Up to the last 6 mos., I got 26 to 28 mpg (higher for longer trips). Now I am getting 20 to 23. Regular oil changes, air/fuel filter changes per requirements. Is there an additive that will actually work and help improve mpg?

Asked by for the 2010 Hyundai Santa Fe
have you had a tune up done?
Yes. Filters, etc. all regularly changed per warranty requirements.
there is more than just filters involved in a tune up have you changed your spark plugs and get it scan tested for codes.the higher the mileage the less your mpg will be because of wear and tear on your engine I would also trying putting injector cleaner in the tank
You have a point there g.g.,I agree.