My brother towed many many miles with a 4.6L 2005 F-150. I rode many many miles while towing with him (21ft Four Winns boat, not very heavy). It was an absolute dog. 35-40mph was it's max up any steep grade. The biggest problem is the 4 speed tranny. The truck never shifts into 1st, and 4th you lock out while towing. You end up basically with a 2 speed transmission.
It will probably be an upgrade over the liberty for brakes, sway reduction, and overall towing ability, but don't expectthe power dodifference to be as noticeable as it seems.