The driving factor behind trucks for 5th wheels, is pin weight and payload.
Typically, the pin weight is 20-25% of the trailer weight (vs 12-15% for bumper pull). Ignore the empty weight and use the GVWR of the trailer as no one tows empty and full timing, you are more likely to be taking a lot of stuff.
Payload vs Pin Weight: Just because you have a truck with a 2500lb payload, doesn't mean you have sufficient capacity to a 2500lb pin weight. Payload includes, people, gear and any bolt on accessories. So if you have a 1000lb of people and gear in a truck with a 2000lb payload, you can only handle a 1000lb pin weight (around 4-5k lb trailer)
- 1/2 Ton Trucks: The payload can vary wildly. It's not uncommon to have payloads below 1000lbs (totally useless for even a tiny 5er). There are rare models with up o 2500lb of payload. At the higher end, these can handle a small 5er...say 6-7k lbs GVWR. As the cost to move up to a 3/4 or 1 ton is negligible, usually better to skip the 1/2 ton trucks.
- 3/4 Ton Trucks: These start at around 2500lb of payload and can get up around 3500lb. For small to medium size 5ers, they can be quite suitable but once over around 10-12k lbs, you will be pushing the payload. They typically have the same engines and brakes as a 1 ton just weaker suspensions.
- 1 Ton SRW (Single Rear Wheel): These will give you a bump up in payload but it depends on the model year. A minor upgrade over a 3/4 ton.
- 1 Ton Dually: Above around 14k lb, this is really what you want. But even here big 5ers can exceed the payload limits (particularly with older trucks where the payload is lower).
You can get away with a lesser truck but it will be less comfortable to drive and you will be prone to more maintenance as you stress the parts. If buying, it's silly to buy a marginal truck.
When you get above 12-14k lb, upgrading to a diesel starts making sense.
