fifth wheel hitches
Take your truck to a scale and find out the actual weight, loaded with people, gas and gear as you would to travel. Also get the rear axel weight. Make sure the total weight is less than the GVWR and the rear axel weight is less than the GRAW (rear axel weight) listed on the truck (on the driver's door jam usually). If so, subtract the actual weight from the GCWR (combined weight rating - I don't remember if this is on the sticker or not; also try your manual or the TRUCK dealer) to find out the absolute maximum you should try to tow. This will tell you what GVWR trailer you should be looking for. Although you will be 'legal' towing right at your max rating, you may be better off in the long run aiming for a weight that is 20% (or more) less than your max.
Never trust anything a trailer salesman tells you; to tell if they are lying, see if their mouth is moving
Also don't trust the dry weight claimed by the trailer; it often does not include options added to the trailer. Even if the actual dry weight is within the limits of your truck, how often are you going to tow with no food, no water, no clothes, no bedding and nothing in the sewer tanks?
One last thing: the trailer and the hitch will add some weight to the truck, so make sure that these weights do not cause the truck to exceed the GVWR or GRAW. A 5ver often has about 10 to 20% of its weight as a 'pin' weight, and I think that travel trailers tend to be under 500 pounds 'hitch' weight, but you will want to verify that as I've never had one.
FWIW, my GMC 2500 HD with 6.0L gas engine claims to be rated for around 9000 pound trailer and a trailer saleman claims that if I had a diesel engine I'd be good to tow the 13000 pounder he wanted to sell me. Consider the source... All I know is the truck is rock steady with a 6000 pound trailer, but has trouble getting it up a hill.