I would bet if you were to get a Sherline tongue scale your actual tongue is pushing 1k lbs. I tow a 32' Passport advertised at 500 lb and it's actually is just shy of 800 lb with all gear (meaning hitch, bars, sway, and loaded...)...see my garage for pic.
Next, have your tried the next link on your WD chains? One link difference made all the difference for me in leveling out. If you hitch up in a driveway, with your truck in the street and the trailer up a bit (as driveways generally are a few inches above the street level) you may need to pull out to level ground to feel comfortable with the extra tension loading (my chains don't even reach when in my driveway because of slope but are prefect on level ground).
No experience with air bags, gut tells me Firestone doesn't have one that works with the Treg's suspension.
One last thing, if your fresh tank is forward, are you full in the pic? Water is very heavy...