A HMMWV has 7.1989 gearing and 37s and will do 65 with a non over drive tranny. That thing has 6.44 gears and 54" tires. It will do better than 45, if the motor can push it. My old M936A2(5-ton wrecker) had the same tires, 7.17 gears and a C series Cummins with a 3100 rpm red line and would do 65 on a down hill, so cruisin at 60-65 would be doable in that thing.