You not only have to consider weight, but wind resistance plays just as much a part if not more in killing an automatic that really wasn't designed for towing in the first place. Pulling a car hauler doesn't catch near the wind as a high profile trailer. I can figure about 20% more fuel when our trucks pull a dry box in a side wind compared to a flat. The R4 700 is a good transmission for smoking the tires around town, but it just wasn't designed for towing. As Hotrod suggests, get the biggest cooler you can find and make sure you can sop the thing. Have you done anything with the suspension on your 51? They weren't the most stable in the world for towing to be begin with.
