I know diesels are the preferred truck for towing, but I'm trying to understand why.

A diesel engine will have more torque (peak power at lower rpm), but often a similar sized gas engine will have more peak power.

Torque at the crankshaft is not as important as torque at the wheel, which we get from the transmission, i.e. the higher reving gas engines power is translated into higher torque at low rpm by the transmission.

So, is the reason diesel trucks are preferred for towing/hauling because they put less stress on the transmission (and therefore last longer), and they are generally more reliable and have better fuel economy? Or is there something I'm not understanding?