Trailerlife.com has tow ratings on their website. One thing to remember, it's not what a truck can tow (towing capacity), but what a truck can safely carry (payload capacity) that counts. You will find, particularly with half tons (150 or 1500) trucks, that they will have impressive towing capacities only to find they will never be able to get that close to towing that much as they are way overloaded on payload capacity before towing anywhere near that heavy.
The label located on your driver door jamb will indicate your payload capacity for an unloaded truck. Load up your truck with all the passengers and items you will take when towing and head to the scales, this will then indicate the remaining amount of payload left for the trailer weight (tongue or pin weight) the truck can safely carry. Tongue weight is normally between 12%-15% of a travel trailer's total weight, and pin weight a bit over 20% of a fifth wheel's total weight.