I’v had a similar problem, done tonnes of eccentrics for 3months and dropped running. Came back to accels in trainers, pain returned. A friend who had similar issues recomended acupunture (it cured his in 2 sessions). I had my first session a week ago, and atm the pain is gone and I’ve been running everyday. My coach massages my calf every training session, and post-acupuncture he said all tightness had left the muscle. He was very surprised. I’m having a couple more appointments and I should think that will be sufficient.