I did the same with my new Limited, Pa to Florida with 1k miles on it and had similar results. 3 tanks averaged 18.5 to 19.5, hand calculated.Drove my 2021 Longhorn 4x4 Hemi E torque to Flordia had 600 miles on it.
Ran 75-80 all the way down 800 miles got 19.8 MPG.
Went another 200 mile south on return got 21.1 MPG to Flordia border
Man was I suprised.