Leaf springs or Torsion bar?

I have a 2000 Silverado which I bought used. I had the leaf springs replaced last year because my rear end was lower (saging) compared to the front end. The problem was solved for a few months but now looks the same. I now find out that it is possible that the front torsion bars my have been cranked to give the truck more front end height. Where are the torsion bar adjustment and how can you tell if the torsion bars have been cranked up? If so would it be better to raise the rear instead of lowering the front?