If you're pretty certain something isn't right, and it sounds like you are, I would suggest taking the rig to a truck spring and chassis shop. They'd be able to diagnose if something is wrong, and in any case probably to recommend what changes if any to make to get a better ride.
Between not seeing the particular rig in question, and having of necessity to rely on somewhat subjective descriptions, and most of us here having no formal training or extensive experience in truck suspension system design or repair, it's a good bet that the advice you receive on the forum will be at best general and inconclusive.