We have a 2018 XLT and towed a 25’ 5000lb hybrid camper from Chicagoland to the Black Hills. With tow haul mode, 87 octane at 70 it ran mostly in 8th gear around 2400 rpm and got between 7 to 7.5 mpg at 65 MPH and ran in 8th around 2200 rpm and 9th around 1800 rpm, we got around 8.7 mpg. I’ll definitely try the higher octane, and check on the thermostat next time I take it in. Honestly my 2004 suburban 1500 with 5.3 V8 in 3rd gear out of 4 at 65 with tow haul and 87 octane was a little better between 9 and 10 mpg. When does the boost come on?