Issue with just going by axle ratio to get your GCWR per X brand engineers. Is you in reality may be wanting a different speed - 35-40mph depending upon gvwr of tow rig, max start grade - 12%, to name two specs in the current jsae tow spec.
I personally want closer to 30% or greater in 1st gear, and my states min speed of 40mph on a freeway grade. Speed is HP spec, grade starts imity is overall low gear plus a tire radius factor times torque. So if you go strictly by GCWR manufactures give you, your drivetrain may or may not be enough for your needs a d wants.
My 02 on the disCUSSion.
Marty