While I towed a 10K fiver for 3 years with a 2011 F150 CCSB Eco, I upgraded to an F350 CCSB Powerstroke. I appreciate the extra 14" of bed length more than anything. If I were to return to an F150, it would have to be the HDPP. That said, a fiver is more stable than a TT and the 2015+ aluminum trucks are reported to be less stable towing than the steel bodies. I am not sure 400 lbs would make that much difference, but it could affect the way the suspension acts.
If you are willing to toss a little money at it, get the LT tires and replace the Timbrens with Sumosprings as they engage sooner and are more progressive. I put them on my SD and they reduce sway on curvy mountain roads.