That is what I did, about a 3/4" plywood shim is what I used at the back from the cab floor to top of the frame. This may be different on other trucks. At the front mount I also shimmed that between the cab mount reinforcement and the frame bracket where the mount bolts on.
This is still a learning curve for me. Today I changed the other front spring. After that operation was completed and everything was tight, I looked at the truck and found the tilt was worse than before I started even though I had raised the cab somewhat.
Slowly, a dim bulb in my skull became a little brighter. Tomorrow I'm going to use the jack to raise the driver side rear frame to see if things look better. I suspect tired springs back there-one or both, and of course it all interacts. I may try using some blocks to try to make the distance from the springs to the frame the same on both sides and see what that does. I would say in hindsight, start by examining spring hardware and springs, and the distance from axles to the frame front and back, side to side. Then move on to the cab mounts.
