I have a 14x7x8 ft. enclosed tandem-axle cargo trailer that I occasionally hook behind my 2001 Double Cab 4x4 (automatic). The heaviest I've had the trailer loaded was just shy of 5000 lbs (just over 10,000 for the GVW). I use a load distributing hitch (even though Toyota doesn't recommend it -- not sure why) because it pulls better than a standard ball, and usually run with O/D off per the manual. I limit my speed to about 60 (mostly to keep rpm and engine oil/trans temps reasonable), but with 4-wheel trailer brakes, I've had no issues hauling or stopping, including a couple of trips over the Appalachians.

I'd think that at 10 mph, you should be able to pull around just about anything that doesn't bend the rear of the frame on your truck, or burn your clutch up trying to get it to move. Good luck!