If you're talking Payload then maybe NO, actually Payload could go down a little with extra length bed due to additional weight of more metal (longer frame, longer bed).
It depends on GVWR rating.
For instance a PowerBoost truck will always have GVWR of 7350lbs, regardless of what trim, 4x4 or not, options, and bed length.
Payload is ALWAYS GVWR minus the As Built Weight coming off the Manufacturing line with whatever trim and options you ordered.
So on a PB truck the longer bed will cost you a little in Payload.
But for other Models/Engines the GVWR may be bigger for the long bed. For instance the 5.0 engine in a 4x2 SB GVWR is 6800 and for LB is 6950. And what they show for the Max Payload (again will be lower depending on options, like Moonroof, etc) will increase by 100lbs.
So once your specific truck is built it has a specific weight, the remainder from that weight to GVWR is your Payload.