The numbers should work if you watch them. The problem comes from the torque management built into cars nowadays. You don't get full throttle from a stop. With drive by wire you only get what the computer thinks it needs. It will ramp up to 95% throttle at most after you are rolling. A good tuner fixes that. The Exploret is a good solid platform with T/H mode and trailer sway control.
I used to tow a 5000lb loaded Award TT that was 27ft total length with a 95 4door Explorer with the old pushrod 4.0L. It did well here in he flat Midwest. With a properly setup WD hitch I think you will be pleasantly surprised at how well it actually does.