I had a '97 F150 4.6L with 3.55 gears and a 4 speed transmission that I used to tow a 24' trailer that weighed around 6000 lbs. The truck handled it great. The engine was a different story. I live in the west near lots of mountains. Just climbing Fourth of July pass (which is pretty minor) would bring that engine to its knees. I'd be going less than 15 miles per hour by the time I got to the top with my foot to the floor. I regeared it to 4.10s which breathed new life into it and allowed me to use that truck for a few more years.
I'm not advocating regearing. And I know the newer version of that engine had more power, but I would be very hesitant to do it again, especially with the larger trailer.
JMHO
