mac stuck at gray startup screen

As of a couple of days ago my mid-2011 MBP has failed to reboot. (I was finally able to get the Mac to boot last night, 1 time, and verified that I had a Time Machine backup of less than a day prior, so I'm not concerned about losing data.)

Here's the failure. First, note that when this problem starting happening I was still using Yosemite, so this doesn't seem to have anything to do with the El Capitan. Initially, the MBP was stuck in an infinite reboot cycle. The gray screen with the Apple logo would appear and the progress bar would make it about 1/3 of the way across before it rebooted itself. I kept hard powering down and restarting without much luck. I then tried to get to the Recovery Console (Command-R) at startup so I could run the Disk Utility and was not able to get that to work either. The only way I was able to get to it, but not consistently, was to hit the Option key at startup, then select the Recovery partition.

With the Recovery Console up I ran a test, using Disk Utility, on the main HDD since all posts I've seen have said infinite reboot loop means the HDD is toast. But the check came back fine. That is when I tried to restart and it worked. I verified I had a TM backup as I said, then proceeded to try and download El Capitan thinking maybe I could get lucky with the new OS. The download was successful, but when it tried rebooting my MBP, you guessed it, infinite reboot loop.

I borrowed a working SSD from a friend to see if the HDD was in fact the problem. I started up the MBP and hit the Option key. My only option was the Yosemite Install I have on a USB key. I selected it, got the Apple icon with the progress bar again, but after making it just shy of half way I get a blank gray screen. It will just sit at the gray screen forever.

This seems to imply that there is something other than the HDD/SSD that is the problem here. It seems to point to some other hardware issue or the boot rom is messed up in some way, But I have no clue where to begin looking.