Tim,
This sure seems like a venting issue still, but my only thoughts in reading through this and the previous post is possibly to determine if the gurgling is being caused by air being pushed into the trap or pulled out of it. I'm going to guess that it's air being pulled in because if it was the other way around it would probably be accompanied by some noxious smells. If you aren't sure, perhaps taping a square of saran wrap over the drain might tell you for sure.
I'm not sure if knowing this will necessarily help diagnosing the issue, but it might. The only other thing I could suggest would be to check for any other air admittance valves that might not be letting air in as they should.
A work-around option would be to install a HepvO valve in place of the wet p-trap. It won't solve the actual problem but it should make the symptom go away as there will be no water to gurgle any longer. https://www.amazon.com/HEPVO-BV1BUB112-1-1-2-Trap/dp/B00NLMPLDU