IMHO, speaking as a 30 year transmission re-builder,
Most late model overdrive type automatic transmissions use clutches that are almost one half the size used for direct drive (3rd gear) for overdrive. Thus you are using half the total friction surface of direct drive that was only designed/intended to drive the weight of the TV along after it had reached highway speeds. This feature let the manufacturers reach increased mileage numbers, keeping the government and customer happy.
Adding an AS that weighs as much or more than the TV to this clutch pack (overdrive) puts a major strain on the clutches resulting in increased heat generated and if carried far enough clutch/transmission failure.
You might be able to get away with this practice (towing in OD mode) if your TV had plenty of power and you were in flat country, buy why risk it?
Transmissions are expensive to repair.
The reason you have tow/haul
or od off
as a selection is to prevent this problem. I would advise anyone towing/hauling anything of more than nominal weight to use these features to avoid future failures.