Why would it sag more? It doesnt sag more, its just more noticable becuase the front of the truck is sitting higher than stock. If your going to tow on a regular bases, or the squat under a load bothers you that much, throw some bags in the rear, should help out nicely.
I love my truck leveled. I threw some one ton blocks in the rear, and a 2.5" kit in the front. Sits about 1/4" lower in the rear now. Cant even tell, honestly.
See if this picture works...