My motto is that tow capacity is like shooting an angry grizzly bear -- there is no such thing as overkill, but there sure as hell is such a thing as underkill.
If you tow a trailer in the western USA you should have a headroom of about 20% in tow capacity to allow for altitude and long, long 6-8% interstate grades. That would put your desired tow rating at 20,000 lbs. That eliminates most all pickup trucks and into the heaviest duty Ford F-450 and 550 chassis cab units with 4.88:1 rear ends.
If you promise never to go west, you can scrape along with the slightly lighter duty units.
In other words, you are in medium duty truck country with your trailer. Freightliners are right at home there.