Trying to understand payload

We are getting ready to upsize our current truck and camper and hit the road full-time. We have been having trouble finding a truck that can handle the payload of most small to medium 5th wheels. Most of the fifth wheels that we have been looking at are in the 29 - 33 ft range and have a hitch weight of 2,000 - 2,400 lbs. Even the Dodge 2500 turbo diesel, which will tow over 17,000 lbs only has a payload capacity of around 2,700 lbs. We see similar trucks all the time towing much bigger fifth wheels than we are planning on towing and are wondering if we are just not understanding how to figure payload? My understanding is that it is the weight of anything in the cab and bed of your truck, including people, gear, etc. Thank you!