Weight Distribution Hitch Adjustment Question

I apologize in advance, I am going to throw a lot of info out at once for a pretty short question... So My wife and I upgraded from an 18 ft. travel trailer to a 26 ft. Fun Finder 265 RBSS. I have a GMC Sierra 2007 extended cab with the 3.73 rear end and we are using a hitch system with a separate sway bar and the weight distribution bars are rated at 800#. The roads getting to the expressway around our house are a little rough, and I have noticed some "porpising" while towing. On the expressway I have also noticed a slight wag in the rear of the trailer from what I am seeing in my side mirror. It is never severe and always corrects itself. There have been some windy trips home that were a bit white knuckle though. The dealer setup the hitch and the guy said that he got it pretty level and was happy with it. He marked the chain link I should be using. Based on what I have read, it sounds like there might not be enough tension on my bars. My main question is though should I be messing around taking in a link when the guy that does this every day said to use the one link?

Some more info: I got new tires last fall. There was a mixup and the tire place and they ended up giving me Load Class E tires. I was okay with that. I have been running them at 45psi which is what the truck calls for. They are rated up to 80 though I think, should I be running them higher? Weight of the gear and people in the truck is right around 700#. Dry weight of the trailer is 5700# and most of my gear is in the front storage under the bed at the tongue. It does have a rear kitchen though and an outdoor kitchen so I know the fridges are adding some weight back there. Fresh water tank is over the axels and while I occasionally pull with water in there I never pull with the gray or black tanks full.

Thanks in advance.

Air the E range tires to more than 45 psi. Try around 60 or so and see if that helps. As to the dealer hitch set up, if the tow vehicle and trailer was not loaded for camping, the dealer's set up is flawed. Most of the time dealers set up a hitch with the trailer essentially empty and nothing in the tow vehicle. That would be an incorrect set up when fully loaded for camping. Be sure you have ten percent of the trailer's total weight on the tongue and 13 percent would be better.