Skip the online towing "guides". I have found the info is lacking and somewhat generic. Really pretty much worthless.
When you have an idea what you want, look at the door sticker for the payload and GCWR of the vehicle. Ask if they have the manual, if not go online and download a copy. The manual will have the most accurate information about the towing capacities and available configurations. With GMs you also need to look at the sticker in the glove box for the RPO codes so that you know what gears it has (you can look up the RPO codes online or have the dealer help you). I'm not sure how to find gearing for Fords, Dodges, or Toyotas.
