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.