Towing with a 2009 Ford F350 6.8 V10 4.10 Supercap LB

OP, use your TowHaul mode as it will downshift the tranny out of OD when pulling hard. With a torque converter you don't need 4.56 gears to get moving. Using TH will let the engine rev more before upshifting and is good for increased engine braking going downhill.