I have a 3/4 HD Chevy truck and a 31foot dutchman travel trailer that weighs just over 7000 lbs. When I pull the trailer there is a lot of sway in the trailer. I have the hitch hooked up right, I think. How many links should up on the distribution hitch? How do I know if I have too many links tied up?

If you have a WDH and your trailer is swaying like a hula dancer, you have problems with your rig's balance.

One... the trailer tongue weight should be about 10% of the trailer's total weight.
Be careful... the way you load the trailer with all your camping gear can upset the best balanced trailer as delivered from the factory.
So ... you've kept the trailer balanced as you load up.
Two ... The WDH should distribute the trailer's tongue weight between the axles of the tow vehicle. Ideally, you have a axle scale for this. But you can use the distance between the fender and the top of the tires to gauge the relative weights. Figure the rear axle measurement should be lower within an inch of the front axle.

Another thought .. All the tires are at the correct pressure ... Right ???

Thanks for all of the suggestions. I did make sure that the tow vehicle and trailer had proper air pressure. I will measure the difference in wheel well heights.

Thanks