Success! Good HD Cable fixes everything.

My Problem

The HD in my 2011 MacBook Pro started to fail. I decided to replace it with a 1T SDD.

My Fix

Swapping the drive was simple enough but the computer still acted odd. Sometimes booting. Sometimes hanging on boot. Sometimes it was fine.

My Advice

Searching the Internet I determined the HD cable was most likely not up to the demands of the new SSD. I first ordered a cheap replacement from Amazon that didn't work. Then I did what I should have done in the first place. I went to iFixIt and bought the proper cable... which works perfectly. Don't try to save a few dollars when you're buying important components for your computer. It's tempting but you do get what you pay for.