If you are having stability issues, first thing I would look at is your setup. You don't mention what the payload of your F150 or weights of your trailer. They are quite a few forum members that are towing the 28BHBE with properly equipped half tons without issue, myself included. If your packing habits require a 350/3500 and your are willing to pay the additional expense of a diesel, you'll love the extra 400 ft/lbs of torque when towing, but trading your new F150 unnecessarily can be an expensive proposition. Stability issues, when towing within specs with a new F150, are the result of not having an adequate hitch and/or an improper setup.
2015 Eagle 284BHBE
2010 Ford F150 XLT 5.4 Maxtow, Coverking Seat Covers, Putco LED interiors, Kenwood DNX571TR GPS, Kicker Powerstage, Weathertech Floor Mats and Window Vents, Line-X, Firestone Airbags, Michelin LTX-MS2, LivewireTS 5 Star tuned, Propride 3P