Hello, I'm curious about the trucks that tow heavy loads of the double overdrive ratio.

I would Ponder a gear pick of a 1:1 ratio for cruise RPM and Tire diameter for the final gear choice.

I would not tow heavy in anything in overdrive ratio and expect the trans to live.

Overdrive Planetary are not big or heavy duty.

68RFE has a 3.23:1 first gear ratio, a 1.83:1 second gear ratio, a 1.41:1 third gear ratio, a 1.00:1 fourth gear ratio, a 0.82:1 fifth gear ratio, and a 0.63:1 sixth gear ratio