I still have that 16' X 7' high Featherlite Stock bumper pull trailer, and still have the "loose load" problem with it.  I thoroughly checked out the tires (Westlake Load Range E 10 ply brand new) and they don't seem to be the problem by way of being insufficient or faulty.  If the trailer is empty, and I am running down the highway, I get pushed around from wind or big rigs.  If the trailer is four horses full, I get waggle going beyond 50 MPH.  My partner says its my truck.  Its a 4X4 Dodge Ram 2006 2500.  My friends say its what you would expect unless you put load levelers on the trailer.

My truck does slouch under less load that I would expect (firewood loads).  Its a double cab 6' bed.

Comments welcome!  I plan to sell the Featherlite and want to make sure I don't pass the problem along to someone else.  I hope it IS my truck, or simply that you need load levelers with this length and size trailer.

My past experience, by the way, is shorter bumper pulls (never a problem even to 14' with three horses in it).  It surprises me that my 14' X 7' tall Moritz, with 3 horses or no horses, pulled straight and true, yet two feet more and a Featherlite and I am all over the road?

Thanks for your input.

With that much weight pulling off the bumper, you may something off this page....

http://www.etrailer.com/dept-pg-Weight_Distribution-sf-WD_With_Sway_Control.aspx

That's what I am thinking, too. If so, the Featherlite trailer moves on.  I don't want to mess with sway bars and weight distribution hook ups; not the expense, and not the extra step to hooking up.  Been there/done that.  Will just switch to a gooseneck.

     Just something to ponder....  we used to have a F250 that would squat horibly with a bumper pull 3H SL, and found that the problem was actually due to the highth of the hitch / bumper once loaded.  The tounge weight caused the trailer to squat, and then put more weight on the front set of trailer tires than on the rear.  After adjusting the bumper highth with the air bags on the truck, we were able to remove all the sway. 

    One thing about using the sway bar (we use one on the wife's concession trailer), the sway generally starts as very minor and gradually increases in a typical harmonic motion.  It takes very little resistance to stop the sway at the onset, vs alot more at the point of dramatic sway, and the sway bar does exactly that.. stops it at the conception..