Your VO is basically my set-up as well....VO tank, pump, filter, CV on manifold (your T), FPHE, TIH along frame, manifold in valley, split to heads. Off the manifold inside box (CV located), splits to purge. Like you, fast purging.

D2 side is completely stock besides the CV's on D2 factory lines at heads.

Take a gander at my wvo album, all my items are consumed in the box (CA smog for the reason all items in box). I cant see where/why i'm havingthis issue, unless i'm purging way too long.

My idea is this...3-way between VO and D2, pump, 3-way, (split d2/vo to respective lines), vo filter, fphe, tih, manifold in valley, split to heads....D2 side will be off tank..3-way(to feed the d2 pump if vo pump craps out), pre-pump filter, D2 pump, C.V., manifold (with CV inline off the 3-way after VO pump), filter bowl, split to heads....gonna snap pic of drawing and post to album....