another dead overdrive unit

I don't understand the "no towing" recommendations. When we drive to Lake Tahoe we climb 5000 ft on I-80 at 65 mph for ~30 miles. Ditto for anyone leaving the LA Basin. Isn't that as much or more load for the drivetrain as towing on flat ground? You do see cars on the side of the road steaming every 1/2 mile the first hot day of the Spring, but that is usually because the fools didn't check their coolant all winter. Our 2002 T&C minivan has AWD and the factory towing package, but as best I can tell that is just a trailer hitch and a power steering cooler (why is that needed?). I don't recall the radiator being a different PN (replaced recently). I mentioned that I occasionallly tow a 2700 lb trailer with it and a mechanic said "I wouldn't". The most important thing is that the towing vehicle is heavier than the load and there is enough weight to keep the rear tires from slipping. I can't see how towing on the flatlands would stress most vehicles.