what to do?

[96pappy]

i've got a 96 gmc 1500 ext cab short box. Currently installing shackles, i say currently because most bolts were rusted in bushings and i had to cut off bolts to remove leaf springs and shackle. Doing this i managed to narf up the leafs pretty good. Now i'm thinking of upgrading to 5 leaf springs in the rear, since i always thought the rear rode too soft. Or is there anything a spring shop can do to these springs and make a 'firmer' ride? Are they repairable?

Thanks