Reading through the thread, I'd say you need to work on running fast & relaxed.
Here's some ideas for your interval workouts, worked for me to go under 5:00 as a master.
Warmup: 2 - 3 mile slow run then 5 @ 80 meter stride, the first one a 6:00/mile pace and the last one @ 5:00 per mile pace, all as a warm up.
From there, design a variety of interval workouts, and run up to three per week.
For fast relaxed running, try a series of 200 repeats @ 35 seconds, with a half lap jog between. See how many you can do. If you do the workout a few times, they'll get quicker, and you'll do more repeats. Focus on relaxed rhythm. Yes you are working hard bu you are relaxed.
Another workout, don't forget the standard miler workout 8 - 10 x 400 at race pace with a lap jog between.
Other days, mix in some longer intervals too, 800s, 1000s, 1200s, with longer intervals. Gets you strong as heck.
Racing, plan a series of 3 - 4 mile races over a month or so. Once your racing legs get going, improvement comes. Rest properly before races. The latter races in your series will feel easier than the first couple, and you will be running faster.
I know this is obvious advice, nothing new. It worked for me. I could sink a mile under 5 minutes until I was 44 years old. The workouts are (easier) variations on what we did in a Div. 1 middle distance program at the dawn of time. Good luck!