SATA 3?

Why is Samsing Magician telling me this? Do I need to install separate SATA 3 drivers? I never had to do this before.

Check the manual for your board. Not all SATA ports are created equal. Make sure that the SATA port that you are plugged in to is SATA 3 6Gb/s and not SATA 2.

Alternatively, make sure that the SATA cable is seated firmly and/or replace the SATA cable.

Thanks for that! I think it ended up being some drivers I did not install. Previous install used a CD that came with the motherboard; this time I thought I'd just download stuff from the website and obviously I missed something. Went back, clean install, and installed drivers from CD first then updated online and things are working better now.

Drivers for what? The motherboard? I've seen boards that use a marvel chipset that needs a driver to work but usually it works or not not working at a lower speed. At least in my experience.

Yeah, it seems so. The only change I made to my install procedure was to install from a CD instead of installing the drivers manually, so there must be something on the CD that I missed --- looks like something called Asmedia 106X SATA Controller.