Quite typical, I went through it just by dropping weight and higher better quality mileage. Most people hit it after 1-3 years of constant improvements when its easy to get quicker, but we all reach our own standard where even standing still is hard work. Thats when talking with others, getting a coach, clubs, mixing it up is needed.
There's just no one cap fits all approach.
I think m next increase will be a more stable life, better diet.