Who did you get the springs from - I'm wondering if they sold you the wrong springs? Some vendors sell nova/ventura parts and pass them off as camaro/firebird parts or Gen II. Even if they're the same length and width, the spring rate or arc may be different.

I recently R&R'd my sagging springs with 4-leaf [80-335] springs purchased from General Spring in Kansas. The new springs got me back up to stock height.