using this tool
https://ecomodder.com/forum/tool-aer...resistance.php
and these variables-
Vehicle weight: 2812.3 kg / 6200 lbs
Crr: .008
Cd: .35
A: 2.9 m2 / 31 ft2
Fuel energy density (Wh/US gal.): 33557
Engine efficiency: .28
Drivetrain efficiency: .95
Parasitic overhead (Watts): 0
rho: 1.225 kg/m3
I don't think you can consistantly get the MPG you want with aero mods alone.