I don't have a AT4 but I'll throw in my experience with my 2020 Chevy HC, CC, 6.2, 6.5' bed, max tow pkg. trailer mirrors. I've been doing mostly highway travel with this truck since I bought it in Feb. Been making 300 mile trips, 60-70 mph and getting 21-22 mpg. I'm happy considering the power available. Part of me still wants the 3.0 Diesel though