I believe all FX2 F150s came with 3.73 axle, but you can look at another sicker on the driver's door jam for something call an Axle code. That can be decided to 3.15/3.55/3.73. Regardless, you'll be a lot happier towing in the 6k dry range as that goes up to 7000-7500 loaded with a family's gear and 1000 pounds of tongue weight. Family in the cab and a bed full of gear eats up the payload.
I have spent a lot of money on extras to my TT that the $600 WDH doesn't phase me. A WDH is required for your truck anything over 600 pounds of TW and 6000 pounds trailer weight. Besdies that, my experience is that anything over about 400 pounds on a half ton will benefit from a WDH. Your selling dealer will sell and install it. I highly recommend one with integrated sway control like krobbe listed.
