ive never had any problems pulling with an auto. i have been pulling a 3 car wedge trailer 53' for over 10 years now. i use a 1 ton ford with 7.3L powerstroke the truck my company has me in now has 150,000 miles on original trans. the 3 trucks before this one all ran to 250,000-300,000 miles all on factory trans. i live in central utah and any road i take out of where i live i have to run up hill. never a problem and i do not push the OD button i let the trans do the work and never lost one yet. the trucks are registered for 32,000 LBS. and i frequently haul loads that push me towards that number.
i will pull with an auto any day.