Thought I'd send an update.
I did get the system working. Seems to be working properly and consistently as well.
The issue seems to have been resolved by doing a factory reset on the SP.
The system originally came with:
Oracle PN: 511-1152-01/Hynix HYMP151L72CP4D5-Y5 AB
4GB FB DIMM 1.5v
I then bought and tried:
Sun PN: 511-1228-01/Samsung M395T1K66AZ4-YE68
8GB FB DIMM 1.5v
I had the same issues.
I then bought:
Sun PN: 501-7954-01/Micron MT36HTF5122FY-667E1D4
4GB FB DIMM 1.8v
Again I had the same issue.
I had reset the SP several times. I had to originally when I bought the server as I didn't know the password for root.
I tried reflashing the firmware but it wouldn't because the system was already at the same version as the latest available version.
The coin battery was also dead on the motherboard as well but I didn't think much of it.
I then replaced this batter and did a factory reset again on the SP.
At this point it all started working properly. I've run though every scenario I can think of and it all works now.
Rebooting.
Power down/Power up.
Reinstall Solaris.
Reinstall Debian.
Drop power mid boot.
It passed POST and boots up perfectly each time.
I also went back through all the RAM I had and the systems worked perfectly regardless of what RAM I had in the system. So it seems the actual RAM was never my issue. So now I have lots of spare ram modules! ;)
Thanks for all the help getting this one up and running!
Especially thank you to Tony for all your help!