Yes this can absolutely be done.
you'll need to jack up the front of the truck so the front wheels are off the ground.
At the rear most part of the torsion bars there is an adjustment bolt that adds pre-load to the torsion bars.
Tighten them each evenly by a few turns. and set your truck back down on the ground. It's recommended that you get an alignment after a torsion bar adjustment.
Be aware that once stock torsion bars start to sag, they will most likely continue to do so after even cranking up the stock torsion bars. Also cranking up the stock torsion bars will result in a stiffer ride. Replacing the torsion bars with aftermarket ones by Sway-a-way or Calmini is recommended.
