[GregK]

That's usually an indication that the tongue weight is too light. Try letting the equalizer bars off a bit. It's often misunderstood that cranking the equalizer up is better when reality is the equalizer setup is to keep too much tongue weight on the back end while still keeping a controllable weight.

 

[GregK]

It's a balancing act that you need to figure out. The way a trailer pulls depends on the weight ratio from front to rear of the trailer combined with the tongue weight loading the suspension of the tow vehicle. If there's too much weight forward or back on the trailer you're going to end up with a tongue weight distribution issue with the tow vehicle. When the trailer is empty it should be designed so that the equalizer bars are not used and it pulls perfectly. It is possible that you have the incorrect rating of hitch for the trailer too.

I'm not suggesting that you don't know how to set the hitch up, but this site may help. There's a troubleshooting section too:

Common Weight Distribution and Sway Control Questions | etrailer.com