Just wanted to return here to wrap up this thread for anybody else that may be researching a similar issue.
I had identified which memory stick was "cold crashing" and used the good one to test the slots. All week I used only the good stick and did not have any crashes. New memory has arrived. I have installed it along with all peripherals and all my software. I have not had a single crash since.
My true symptoms turned out to be that my computer would BSOD when the memory sticks were literally cold. The BSOD's would often indicate different causes. Memtesting did not show any fails because as soon as the memory warmed up it worked fine. It literally had to be quite cold (like left overnight with case open on colder evenings in Colorado). As soon as the system was powered on for 15-30 seconds it would be warm enough to operate fine so it was only after starting memtest straight away in the morning I could detect to issue.
zigzag, thank you for your help and patience. I was pulling my hair out trying to figure this issue out and your guidance saved the day! This was the first time I have buid a computer and thought I must have had really screwed the pooch but had no idea how. At least I could use this as an excuse to bump my RAM from 8 to 16
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