I don't doubt for a minuet that they can tow 11,lbs, it just depends on how comfortable you want to be while towing.
I use to tow a tag trailer that weighed just over 10,000lbs with a 1500 V-8 Chevy short bed. Sure it towed the load, but it was not comfortable. I was always on the lookout for any situation where I had to stop quickly, and the take off power was not very good. Once it's rolling, sure anything can tow, but take off and hills just kill the thing.
The diesel, with it's HD chassis and gobs of torque is so much better suited for towing. The trip become fun and your not all knotted up while driving. You know you have the power to merge, pass and motor down the highway like nothing else out there. The brakes are designed to handle the extra load and are very comforting, throw in a exhaust brake and there is no hill to fear.
Ford upped the towing claim to be on top of the 1/2 ton truck wars, they had to do it to stay ahead of Toyota. Ford it really on the ropes, and needs this extra advertising gimmick to sell there trucks. Funny thing is I would believe that Toyota could actually handle the load better then the ford, they have always been more honest in there fuel mileage and performance claims then the domestic market has been.
Like anything else, it all comes down to what works and feels best to you. For me and my new 16,000lb trailer, it's diesel all the way. I run the 4. 11 gears and love the extra torque they supply. For me, towing ease takes precedence over maximum mileage. But don't purchase a new truck with there supper high 3. 42 gears and expect the same performance, those gears are for the commuter crowd that only use there trucks to go back and forth to work, not work or tow.