Nugget hunting certainly ain't easy. If it was everybody would be doing it. It takes lots of persistence, patience and time with your machine in a gold area to find gold metal detecting. Sometimes in some areas thinking outside the box equals success. You went to some really hammered ground at those locations which adds to the difficulty. I've been very successful over the years, and have yet to find a nugget at the LSD area. Although I can't say I have spent that much time out there myself.
A couple questions for you: Did you get any training with your GPX? It can be difficult to master that unit with so many options. Did you happen to hook up with a local to hunt with? Sometimes hunting with a person that has had success can shorten the learning curve.
The best advice I can offer for somebody coming to Az. for a short duration to detect gold, especially on club claims, would be to forget hitting the obvious spots and think about trying the not so obvious possibly over looked areas on a claim.
The gold is still out there, however the easy obvious spots on the claims have been hit many times before. You obviously found boot tacks and such so you are on the right track, but it takes a lot of time and dug trash to succeed at metal detecting gold. Dennis