My one-ton passenger van has a 3000 pound payload and a 6000 pound towing capacity with the mid-size V8. The limiting factor is GCWR rather than tongue weight, which is the problem with SUVs and 1/2 ton pickups with high tow ratings.
If you buy with the right engine (6.8 V10 on Ford, Duramax on Chevy) a one ton van might go to 10,000 pounds on the towing capacity, but as tongue weight might go up to 1500-2000 pounds, you then have to start thinking about balancing what you carry and tongue weight, to stay within that 3000 pounds. Just as you do for a one-ton pickup.