The 1999 towing guide shows your configuration is rated at

13,100 lbs for 5th wheel towing, when equipped with auto trans, tow pkg, and 3.73:1 rear axle.

I don't know if that figure changed for 2000.

My configuration (see sig) is rated at 13,800 lbs. You are giving up 700 lbs of towing in exchange for your 4wd and crew cab vs. my supercab config.

That is just rating. What these trucks can actually pull is much more, but at the cost of safety and increased wear on your drivetrain components.

What year was the 'new' truck you saw? The newer (2009+) trucks have substantially higher towing capacity, especially if it was a F450. The 2012 line is rated up to 24,400 lbs of towing for the F450, and around 16,000 for the F250/F350 SRW and the dually bumps the cap to 22,000.