Do I need a weight distributing hitch?

After once owning a 2001 Expedition and pulling a trailer with a dry weight of only 2500 lbs (probably around 4000 lbs the way we loaded it), I can say with confidence that you'd like having the WD hitch and sway bar. The rear suspension on those vehicles aren't like with a truck, but more like a car for the ride. While it won't necessarily sag a lot, you'll bounce hard in dips, RR tracks, etc., without the WD. With the WD, though, it's solid as a rock and you'll likely forget the thing is behind you, that is until you tally up what you paid for gas.