With my 555 2003 LWB Auto 4. 10 unloaded (2 months new to me), using dino oil, all highway driving, I got 17. 7 mpg with the tail gate down (6 wks ago).
With syn oil on 1 tank, I did mostly (85% guess) highway, I ended up with 18. 2.
I'm taking another road trip this weekend (same as before)...