I asked my concrete guy to try and keep floor pretty much level except where it gets near floor drain. Its not good at all.I had about the same slant on my floor. I put shims in, I think it was the way to go. It will bug you forever if you don’t.
I put rubber pads under the 4 posts,they dont make the creaking and popping noises so much when it flexes. It does still wander around. Every month or so i have to push it back into place. I may drill 1 hole in each post to keep it from moving.