I've got a 85 f150 its got 3 inch block lift and I think I need either new leafsprings or new shocks I only say that cuz when I sit in the bed I weigh 350 it the back end drops about 6 -8 inches and when my buddy who weighs about 160 sits on it Jt drops about 4 inches also when I'm goin down the highway and I hit 60+ it bounces around also if I have to slow down real quick it feels like its bouncing around and I kinda go sideways not completely sideways but enough to where you can feel it
Do I need to replace my leafsprings or shocks or both

 

If it's bouncing around like that, shocks for sure. 6-8 inch drop when you sit in the bed... you might consider replacing the leaf springs too or at least adding a leaf. You could put the shocks in first though and see what you think.

 

Could I replace the shocks and add shims to the leafs ?

 

Yes on the shocks. Not positive on what you mean by "add shims' but if adding shims is the same as adding an extra leaf, then yes. From what you said it sounds to me like someone took a leaf or two out of your leaf springs in the past sometime. If that's the case it might be easier to find a set of springs at your local wrecking yard and just change them out all together. Unless you've already got some extra leafs hanging around. Just a thought.

 

And be sure to check out the shackles and shackle hangers for cracks or breakage, they would cause some scary sway.

 

Well I've got to go to my yard this weekend and ill check out how much they want for a pair of leafs how many leafs came stock just from memory I think there's 5 or 6 on it