Most who use a weight distribution hitch need to lift the trailer tongue AND the back of the truck to attach the weight distribution bars. If you size it just to lift the unattached tongue, it will not be sufficient to lift the back of the truck also to attach the WDH bars.
My tongue weight is 780 lbs. and the 3500 lb. tongue jack is slipping a gear (probably a torque limiter) when it gets near the height I need to attach the WDH bars. If I ever have to replace mine, I will go to a 4500 lb. rated jack.
