I'm guessing this is another case of someone who just isn't used to what a hard working engine sounds like.
Without a load, most of us drive around at minimal RPMs and it makes us think anything higher is bad. It's not. You can use your RPM range without hurting the engine. They're designed for it.
As mentioned, find out where your engine produces it's torque and use it. Most of these 5.3s make their torque at higher RPMs. It's not bad. It just is.
I think you're fine. Swapping gears is very expensive and you'll not notice much gain from it