towing mileage of trucks

I think many people fail to understand that the right axle ratio for the job means the truck will downshift out of the overdrive gears when the task gets heavy. Its better to run high HP through 4th gear and slow the drive axle down a little with a 3.55 ratio rear end than it is to run that HP through an overdrive gear to speed the output shaft of the transmission faster only to slow it way back down in the rear end with a 4.30 ratio. The purpose of the overdrive gears are to slow the engine down for fuel economy when high power is not required. It's not a bad thing for the truck to downshift on the hills or even to lock out 6th gear when towing heavy. These trucks make so much torque that they can get a heavy trailer rolling without needing 4.30 gears.