Randy, the one thing I would say is I suspect your potential lies well on the other side of 3:30.
We can all analyze this to death if we want and probably find a lot of things that may or may not be limiting you. One thing stands out, though. You’ve been running for 2 years and you’ve been running a marathon every 6 months throughout that time, including a marathon within your first 6 months based on what I see. Maybe you’re marathoning yourself right into the ground. You didn’t take time to build up to the distance when you started out and you currently aren’t giving yourself any time to back off and regroup. Is there a reason you’re running marathons every May and October?
You’ve been running for 2 years. Rest assured, you are not close to your ultimate potential yet. I’d guess you have at least 5 years before you have to worry about how close to your potential and before anyone could offer anything other than a complete shot in the dark as to where your potential lies.