Just about all 250/2500 trucks are limited on payload due to government regulated class system and NOT due to the limitations of the actual truck. The class that 250/2500 trucks are in is maxed out at 10,000 lbs GVWR so no manufacturer CANNOT rate their 250/2500 truck past that. For Canada it is 9,900 lbs which is why the very same trucks here that have a 10,000 GVWR over their have a GVWR of 9,900 lbs. Since payload is a trucks GVWR minus its curb weight and because the class the 250/2500 trucks are in have a max GVWR of 10,000 lbs due to government regulations. The truck's payload will be lower because the maxable government allowable GVWR for that truck class is much lower than the class the 350/3500 trucks are in.
Perfect example would be the 2015 F250 and the F350. Here are the specs for each that can be found here....
Super Duty Pickups
F-250/F-350/F-4502015 F250 SRW 6.7L 4x4 172.4
GVWR: 10,000 <--- Max GVWR for class 2 10,000 lbs
Weight: 7,668
Payload: 2,400
Front GAWR: 5,600
Rear GAWR: 6,100
2015 F350 SRW 6.7L 4x4 172.4
GVWR: 11,200 <--- Max GVWR for class 3 is 14,000 lbs
Weight: 7,720
Payload: 3,550
Front GAWR: 5,600
Rear GAWR: 6,290
Keeping in mind that to Ford(and all vehicle manufacturers) the GAWR is in Ford's words "determined by the rated capacity of the minimum component of the axle system (axle, computer-selected springs,wheels, tires) of a specific vehicle". If that is the case, why does the F250(which has the same frame, tires, transmission, front axle/suspension, and brakes) has only a 190 lb difference in rear GAWR yet has over 1,000 lbs less payload? That is because the F250 is maxed out at 10,000 lbs for its class and the F350 can go up to 14,000 lbs. It has nothing to do with the actual carrying capability as some suggest, and has more to do with an archaic truck class rating system the DOT uses which modern trucks far exceed. Then there is the registration fees that most have that sky rocket for any vehicle past 10,000 GVWR.
So keep this in mind in your search for a new TV. Although if you do get an F250, go with the camper tow package. It is about a $160 upgrade, but it adds an upgraded suspension with more leaf springs and a rear stabilizer bar on F250s essentially making it the same as the F350, but with F250 decals(still with a 10,000 GVWR though).