Towing course for dummies-
Install weight distribution hitch for equal weight. This does not result in a level tow, unless the weight loaded onto the vehicle is within the original specs for ride height.
Level towing- this is achieved through the suspension dynamics, most easily through air suspension (redirecting weight into the chassis and front axle, or having an equal amount of pressure at each wheel if 4-wheel air suspension). You can have level towing WITHOUT a WDH, if you have air suspension. Without, it would be impossible to have truly level suspension. Most vehicles with traditional coil/leaf springs have the rear raised up during normal unloaded operation, to accommodate such load that they are safe at high speeds due to being level.
TLDR: get a WDH, set it up correctly, and still have some sort of sag. Add air suspension, or get something with air suspension already equipped (this DOES NOT increase towing capacity by the way) and you can achieve a completely level vehicle (expedition) with either 10,000 pounds or 2,000 pounds behind it.