Suspension question

[tommy217xxx]

I have a 76 gmc 1500 that rides like a tank. It has a flip kit in the rear and drop spindles and lowing springs in the front. The shockers were never changed. They have about 4" of travel. The rears are almost 45 degrees from vertical. The truck also has 6 leafs per side in the rear. This is how the truck was when I bought it.

I'm working on the truck now and it's time to change the suspension around. I know I want to change the shocks. I'm gonna get shock extenders and new leafs for the truck. I'm lookin for a smooth ride and the only thing I'm hauling is ass around town.

I've done a search but I'm lookin to the most current setup. What should I get? Should I get my leafs from local auto parts or order from summit. What extenders should I get? Do I need to extend both front and back? Any recommendations would be great.