Post #4:
Is there a way to verify that it is the outlet and not wiring? I have a multi-meter.
The important thing to keep in mind when attempting to test one of these type receptacles is again the fact that you can run tests of the receptacle in question, but unlike a regular home receptacle one of the major (failure) facts of this type is that the "pincers" may not be making contact with the metal of the conductor when the receptacle is sandwiched and tightened down. So you can test the receptacle all you want, if the pins (pincers) are at all damaged even at the slightest bit the pincer will fail to make contact with the metal inside the conductor (failing to fully penetrate the insulation).
You can test the GFCI by doing a continuity check. Place the meter on "ohms". Place one probe in one slot (either the hot, neutral or ground) place the other probe on the corresponding wire of the GFCI if you get continuity on all three then the GFCI is functioning correctly. But you would have to be sure the the gfci is not tripped itself first. even if it is not hooked to power. if it is tripped you will not continuity.
if you touch on probe to either the hot, neutral or ground and the other probe to the other two and you get continuity it means something ain't kosher.
Again, you could be beating yourself up attempting to track down this issue.
If it were me and I had to do it. What I would first due is eliminate the possibility of one of those darn crappy all in one receptacles as being the culprit.
I would:
Remove all of the receptacles in the path of the last known working receptacle (removing this one also). Then wire nut my hots, neutrals and grounds together respectively at each receptacle location. Go to the end of the circuit (last known non working receptacle). Take those conductors, hot, neutral and ground. Take your multi meter, check hot to neutral, hot to ground, neutral to ground.
If i get 120 v hot to neutral and hot to ground then I know it is one of those stupid receptacles. reinsert one receptacle at a time by going to your first. Remove the wire nuts. place the conductors in the all in one. go to the end of the circuit. repeat the test above. if you get proper power then reinsert the next receptacle down line from the last newly inserted receptacle. repeat this process to the end; the last receptacle. doing this will eliminate the fact that the pincers are not the ultimate culprit. But also, when inserting the new receptacle and testing the end of the circuit and then you know that newly inserted receptacle is functioning, place that newly inserted receptacle in the wall and anchor it. again test the end of the circuit. this will ensure that while working with that newly inserted receptacle that while you were handling the receptacle and anchoring into the wall that the pincers did not somehow come dislodged and lose you continuity of the circuit or you can end up repeating this all over again. If these were regular receptacles i would just run the initial test and using new $1.5 receptacles and save myself the headache.
And of course other than testing at the end of the circuit for voltage reading at each step be sure to turn the proper breaker off