A number of people have said that the Taco has a 650 lb tongue weight limit, but I can't find anything in my 2011 manual that says that. The receiver itself only says "see owner's manual".
The manual says that the tow limit is 6500 and to keep the tongue weight close to 10%, so you might get a 650 tongue limit out of that, but it is a stretch.
The manual gives limit for tow weight, GCVR, GVWR, and each axle. I figure that with a properly adjusted weight distributing hitch and nothing in the truck except two people, I could get the tongue weight up around 900 before I hit either the GVWR or rear axle limits.
I'm thinking about a travel trailer, which generally have closer to 15% tongue weight, so I could be above 650 tongue and still well below the 6500 tow capacity.
So where did the 650 lb tongue limit come from?