I would like to lower mine too. I mesured mine -FR 32" Rear34" so I was thinking of getting a ground force kit from styling concepts I think they got a few choices as to how much drop you want .THERE IS ALOT ON LOWERING IF YOU SEARCH BUT FEW ON 03 -04
The "best" portion of that is very relative. How much lower are you looking to go? Is the truck a driver, a dragster, a corner carver? Put up some more detail and we can help fine tune the answers. The 03 and 04 sits about 1 inch higher than earlier trucks, so bear that in mind as you're looking.
The search is good advice though - there was another lowering thread just yesterday.
Well My 02 Just Had The Springs And Rear Shackles----i Just Got A 03--it Is Higher In Back-------i Was Thinking Springs In Front And Hangers And Shackles In Back---but I Hear A Lot Of Different Answers
If I were to do it all over again (which Im trying to do) I would get 99-02 Leafs and shackles, or Hotchkis rear leafs with shackles. I like the way my truck rides up front with 1 cut coil out of the factory coils (2in drop) The rear I removed 2 leafs and Chevy Shackles, The height is perfect but the ride is a bit too soft for my liking. I bet its not nearly as bad with just one leaf removed. But probably lifts it 1/2-1".