Sounds like the springs are shot. Rearching them will help, or at least for a while. Rearched springs have a tendacy to eventually settle back down to where they were to begin with. For the cost, you would be ahead getting new springs. Replace the shocks at the same time.
On the rearend, I would advise against the 2.73 gear, given the transmission you're running. It's too high of a ratio. You'll find that you'll lose gas mileage, especially in traffic, as there's not enough gear to get the truck rolling. With the rear gear and trans you currently have, your final drive is approximatly 2.36:1, with a 2.73, it'll be 1.9:1. Great for a high speed highway cruiser with a torquey big block, not so great with a smallblock. It'll get the engine below it's ideal powerband, which will kill the mileage.
