Whelp after I replaced one of the valves, the MPV, the manifold, grids and the o-rings, I went back to the filter and found that the manifold wasn't all the way on the stand pipe. Which is odd because that's how it was when they opened it, and then I must have repeated it when I replaced them.
So I'm out a few hundred bucks, replaced some of my equipment and have a much better understanding of how all of this works.
Just vacuuming the DE out of the pool now but I'm thrilled that's it's finally working. I added enough DE the first time, so I'm thinking after it's all vacuumed up I should be good? Or should I just backwash and do 80% to be safe