For a Bumper Pull you want between 12% and 15% of total current weight of trailer on the tongue.
I went to the AMPED website. 28FS.
Dry Weight - 8692
Hitch Weight - 1318
That stated hitch weight is 15% of the total dry weight.
Payload Capacity (I'm assuming this includes Fresh Water and Fuel) - 4208
GVWR - 12,900 (4208+8692=12900)
Assuming you are at GVWR when loaded, 15% of GVWR means the tongue weight should be 1935 lbs when loaded. I'll bet you will find it is much lighter than 1935 lbs when you check your actual weights when fully loaded and hooked up.
One of the keys is it towed fine empty. So the toys in the rear might be lightening the load on the tongue. Empty or full tanks have an influence on tongue weight.
Move weight forward (toys). Front of trailer should be slightly lower than rear. Air up your TV tires. Might need to take some air out of the air bags. Might need to loosen up the Blue Ox bars. You are probably fighting the inherent instability of a lifted truck as well.
