Check your hitch receiver, for it's weight rating. It will have a stamp with two numbers, one without weight distribution, and one with. It's possible, you're exceeding the weight rating on your receiver.
You say the trailer weighs 5500 lbs. At that weight, your tongue weight is around 790 lbs. If that is dry weight, your loaded numbers would be considerably higher.
When you hang the tongue weight on your hitch, it adds weight to your rear axle and takes weight off your front axle. If there is too much weight lost on the front axle, it can cause trailer sway and steering control issues. The primary purpose of a weight distributing hitch is to restore lost weight on the front axle.
Your owners manual should tell you the weight at which you should use weight distribution, and the percentage of lost front axle weight you should restore.