..... which caused the entire pack to move away from my body, putting a lot of pressure and discomfort on my waist.
The pack moving away from your body makes it sound like you don't have the load lifters snugged down. The usual way to do that is to loosen up the load lifters and shoulder straps, get the hip belt adjusted right first, then snug down the shoulder straps second, and then snug down the load lifters last. Don't be afraid to crank down on them; they bring the load close to your body.
Then after you crank down the load lifters, the shoulder straps may be a little too tight and need to be loosened a bit.
