Jesse, you’re pulling around 59lbs at 29.5” with a fast bow riser cut past center. Thats a lot of energy with a long arrow/power stroke... Makes a BIG difference on dynamic spine. In my opinion, the 400 results are exactly what I’d expect. Significantly weak, and when you load up the front you’re getting a false stiff. I believe you are minimum .340 & that’s likely with standard aluminum inserts. I also have no doubt you could tune .300s if you’re flexible with insert weight (standard aluminum/50 grain brass/100 grain brass) & length... Of course the simplest thing would be to buy a .340 & .300 shaft and test. When I tune, I start long and am slow to cut very small increments. Also having a variety of field tip weights helps discern where you’re at easily before you cut/finalize. I have 100, 125, 145, 150, 175, 200, 225, 250 and even heavier field tips, plus 5 grain brass washers. You can leave the insert alone at first and get close with combined weight of field tip and insert, then later dial in what insert weight and length go with your preferred 175 grain head... once you’re close, it builds confidence when you screw in a lighter field tip & the arrow goes more stiff, and vice versa when you screw in a heavier tip it goes more weak....