I have a simple GPS fix that worked for me. I'd like to mention that the solution may not work for all but it did work for me after I tried just about every fix possible. For example I flashed back to stock, performed numerous battery pulls, used many of the AGPS patches, made numerous edits to the gps.conf file, reprovisioned my phone, checked different ROMs, uninstalled/reinstalled Google Maps, cleared data for Google Maps and Google Service Framework, and so on.
I tried all of the above methods because my GPS would take forever to get a fix both indoors and outdoors (I know it usually takes longer to get a fix indoors), wouldn't hold the fix while navigating and my GPS apps kept stating "Searching for GPS", would see 20+ satellites but would never lock on to them...man it was really frustrating. I just about gave up.
However, as I was trying to follow another procedure to fix my GPS which required me to pull my battery I noticed that when I removed my back cover that the back frame that has all the screws was slightly loose on the left side. Once I tightened them all up my GPS worked immediately! I've tested for a day and I consistently got a lock on the satellites in about 2-15 seconds depending on my location. My navigation also worked and wouldn't cut in and out.
Like I said it may not work for everyone but I would recommend that if you have a GS3 definitely check the back frame of your phone and make sure everything is secure. I've tried my GPS on the stock and CM 10 stable ROMs and I have achieved GPS locks consistently.
I hope this helps. Maybe this has already been shared but I figured I would post in case some of you haven't seen it yet.
Thank you for the suggestion. It saved me from getting a refurb.