its all about what your truck can carry, not pull. I have a "1500" series fifth wheel and in no way shape or form would a 1/2 ton do the job and stay under its GVWR or RAWR - Mine is similar in weight to what you just purchased.
for what its worth, its not when your going down the road on a flat easy terrain with no wind that is the concern, its in an emergency situation or coming down a large hill and getting hit with a large gust of wind - that's when you'll quickly find out that you don't have enough truck.
that 5er needs at minimum a 3/4 ton truck to be safely towed and to be honest, if you make the leap to the bigger truck you'll be much happier with the towing performance in general.
