Torque convertors will give you 2 to 3 to 1 gear reduction or advantage but only for a short amount of time.  There is lot of heat and pressure developed while they do.  Damage can occur in just seconds if pushed too far.  Towing or hauling heavy loads even in trucks designed to do so. Damage occurs when first starting out. A common problem is backing up a rolled curve or steep driveway.  If you have to give a lot of throttle to start moving your load is too heavy. It can be worse in reverse as most transmissions have a higher gear ratio in reverse compared to low. An example, a 48RE, common in Dodge trucks, reverse is 2.21 to 1 with low gear is 2.45 to 1. If your vehicle and load is such that it doesn’t start moving at half throttle, within seconds, you are risking torque convertor damage.

• When backing over a rolled curve, always go over them, moving and straight, never from a stop.
• Avoid parking on hills. If you do, park so you can start moving going downhill.
• If you have 4 wheel drive, you can use 4-wheel low, as long as you don’t turn your steering wheel (go straight.)
• Don’t use front hitches for launching boats backing up a ramp just one time pulling a heavy boat out of the water can destroy a convertor.
• If you need 4-wheel drive for off road always use 4 low use 4 high only in light snow or ice