Dr Smith is right. Although as another one of Hadd's runners, Hadd would not have us do long runs at MP.
You are super fast twitch and you are running almost every workout at 3 mmol levels and faster. Which is to say WAY TOO FAST!!! There is no way you know this because it feels relatively easy. But you CANNOT store enough of the fuel your body uses, primarily (glycogen) to finish a marathon. So you crash and burn around 22-23 miles.
The only way to know what paces you are running and at what fuel level(s) is to either be lactate tested or use a heart rate monitor
I think it was even written by Hadd in his Phase 1 paper, "how many of us know a guy that can do his long runs at 6 minute pace but when it comes time for the marathon he can't finish it?"
You are such a common story and almost identical to mine. I came to Hadd as a 4:22 mile/16:04 5k/1:16 half. My first marathon was 3:09. At 39 I ran 2:45. I averaged, at most, 55 miles per week. Had I the time (three small kids), I would have loved to run 70-85 miles a week and might have run a 2:30ish marathon.
For god sakes, buy an HRM, do a max test then start running your longer runs, in the beginning no faster than 70% of max. This will be dog slow (and you will want to run faster as faster running will actually feel easier) but you HAVE to teach your body to burn fat as a fuel source and to keep your Anaerobic system quiet. As you begin to strengthen your aerobic system you can add in some slightly faster work during those longer runs. Such as 2 x 15 minutes at 80%, 2 x 20 @ 80%, 1 x 30, etc.
Over time you can bump up the pace a bit to 83% and repeat. Eventually you should get to where you can run 1 x 90 minutes at 88% (which is marathon pace) and where your HR stays ROCK STEADY and does not go up!
I have also coached several runners just like you. It is a process but you have the ability to run 2:30-2:35.
Do not listen to these folks who say to eat gels. While their intentions are good they are not giving good advice for training, only for fueling during a race...