Turns out I was over-tightening my pack straps for 8 years
Hiked the Eagle Creek trail in Oregon last July and my shoulders were screaming by mile 3, so this older guy stopped me and pointed out my load lifter straps were cranked way too hard... he showed me how they should sit at a 45 degree angle and suddenly the whole pack felt like it vanished. Anyone else been carrying their gear wrong for way longer than they'd like to admit?