It's supposed to sag, or at least the rear should drop. In my experience, about 1.5" in about the max for a half ton and a properly adjusted WDH.
Focus on the front axle height/weight, returning to unhitched height/weight. Once you have that and the TT level to slightly nose down, you can measure the rear of the truck. If it's more than 1.5:, you are probably overloaded. Air bags will mask that. But the 2009+ Ram 1500 has pretty low payloads. A family of 4-5 in the cab can leave less than 600 pounds of loaded tongue weight.