I have a 2015 Ford F150 2WD w/Ecoboost, 6 cylinder. I am noticing that when I tow a loaded 3-horse trailer at approximately 55 + mph on the highway it begins to shudder. I can't think of another word to describe it. When I drop the speed back down to 50 or less, it is fine. It doesn't happen any other time, just when I'm towing.
Any thoughts?

 

Well, off hand it sounds like a tire/wheel out of balance on your trailer.

 

I've always had my trailer tires balanced, and every time the tire guys are amazed. I'm always amazed at their reaction as the difference in night and day between 4 balanced versus 4 unbalanced trailer tires, just saying....

 

Could it be wind buffeting? I know some horse trailers are somewhat blunt on the front that could create a shuttering affect at a certain speed.

 

Probably un-balanced trailer tires.

 

It never ceases to amaze me how tire dealers and trailer dealers will tell you that a trailer tire doesn't need to be balanced. When I asked one why he thought that, he said that you'd never feel an unbalanced trailer tire in the tow vehicle. So, if you can't feel it, it doesn't exist?