I went on a pretty bumpy road and noticed while going over trees and stumps my bed was twisting pretty bad as I crawled over tree roots and what not. Is this normal? On a flat surface everything is level, just wondering what the deal is or if that is the design.

 

Some flexing is normal.
Just to be sure, check that all the bed bolts are still there.
The spot welds on the braces under the bed break off as well allowing lots of flex and vibration.
My white crew had some bolts missing when I got it.
This added stress to the other areas that still had bolts, starting some crack in the under bracing.

 

When I got the truck there was a huge hole in the bed from the stacks. I probably should weld it back together. As long as some is normal than no worries. I would say it flexed an inch

 

My bed was so bad you could go the rear edges and lift the bed off the frame with just your two hands and flex it a bit.
The rear bolts where gone and lots of the spot weld where broken.
If you just got it to flex an inch, that is fine.
The factory built some flex into the frames.

 

 

Yup mine was like the ford

 

You can usually tell a 1st gen that's been off road a bit by the dimples the box puts in the cab as the chassis flexs. It's normal. My 78 GMC with a nice rusty bed on the other hand has so much flex it scares me sometimes, but it really works well offroad.