Unloaded, your truck sits at a given height. Load the TC, and it will definitely squat, regardless of what you have for suspension. Overload springs, Timbrens, and all other fixed supports may reduce how much it sags, but cannot return the truck to its unloaded height. Regardless of how you install them, they must compress to take up the slack, and when the compress the truck will squat. To my knowledge, only an air suspension is adjustable after you apply the load. If you are not interested in air bags, then you will have to accept the squat.
Wayne