Also remember that static weight (small open trailer with something heavy) is different then dynamic weight (through aerodynamics, like a 3500lb 20' travel trailer). The short wheelbase of your truck may cause you greif when it comes to larger loads, so be careful and be aware of all the factors while your towing.
I've seen several smaller vehicles with higher payload capacity's (re: Diesel Liberty) that are hooked to very over sized loads (not necessarily overweight) for the vehicle size, rolled/flopped/jack-knifed on the side of the hwy when large winds came up, or they had to slam on the brakes for some reason.