Yes you can take tongue weight off by loading heavy things in the rear... just not too much. Not sure where some are getting that you need 13% as 8-10% is a common number. It's real easy to find out if you do not have enough tongue weight... at 45 mph give the steering a wiggle with your hand on the trailer brake and no one coming in either direction. If it starts to sway, use the trailer brake to slow down and shift some weight forward. Your 5.4/3.42 is on the shy side but by not using OD and keeping your total weight down and the tongue weight down I've seen worse.
Taking a empty TT out is not going to prove much but you can get to see how much it squats your Sierra without WD. What is the wheel base of your TV?
