Sorry to hear about your Mothers passing.....
As to your question: When you say trailer hitch, do you mean a heavy duty hitch made from square tubing that mounts to the frame of the truck? It should have the capacity stamped on it.
Many times the braking capacity of the truck itself is the limiting factor on what you can tow, unless the trailer has brakes.
Check out U-Haul's website:
http://www.uhaul.com/reservations/RatesTrailers.aspx You can plug in your truck data, and once you define your hitch information it will tell you what you can haul.
Or, as they state, "
The allowed cargo weight (the amount of weight you can put in a trailer) is based on your vehicle's curb weight (3,450 lbs.), the trailer's capacity and your hitch system rating."