I think corn or high NSC absolutely could make a difference for those horses in stalls or with limited turnout. IME my horses are much MUCH healthier metabolically, mentally, and physically when they're out on pasture...even if that means they need to wear grazing muzzles. My problem child, Jesse, my roan QH, is almost a different horse after being turned out in a quarter section pasture since January. The pasture has hills, a live creek, and shade trees. It has decent grass. I still feed him his low NSC feed Nutrena Topline Balance and Renew Gold. I still provide free choice salt and supplement him with vitamin e and magnesium. He looks amazing... considering I thought maybe I'd be putting him down. Not sure if he's actually sound enough to do much.... but wow. I still would like to test him, but funds are limited for that when he's showing improvement anyway. Keeping horses more as nature intended them to be kept can do some really really good stuff. Arem, I think I'd go ahead and do the 5 panel and the color test from whomever APHA will accept results from. If she's negative for PSSM, and you still have unexplained issues, I'd look at either testing her for the PSSM variants or tweaking her diet as if she is a variant. That may be as simple as adding more amino acids, vitamin e, fats... worth a shot anyway. Join the PSSM group on FB. They're a pretty good resource. I think some people are lumping all "weird" stuff into PSSM problems, and that is not good, but there are legitimate pathologies out there that need to be addressed. I think it is possible we'll see many more diseases we'll need to treat and test for; we've been breeding too closely for a long time now. I'm a big fan of line breeding, but I also think we don't know what we don't know about concentrating these lines. There's not really that much genetic variability in our stock horses.