Just wanted to update everyone. It's like a miracle.
As much as I wanted to retest and do massive water changes, I haven't yet found the time. When I get home from work I am too exhausted to do anything physical sad to say :/
But yeah, the only thing I did different was dosed some drops of Prime in each tank, left the fan on all the time and just top off 100% RO every day. Tank staying around 74F since then. The deaths just came to a complete halt.
From 1-3 deaths per tank per day, now none. They somehow look livelier too, like even more solid colored and just got a couple berried shrimps today. I guess the Prime helped eliminate the ammonia that have increased from all the deaths and the temp sitting at 74F compared to 76-78F made a huge difference. I guess with MY shrimps borderline is 75F. Each strains are different. Mine consists of mainly PL's and Hybrids so perhaps that is why they are more sensitive.