I've been there too with achilles tendinitis. I agree with the previous comment, slow and controlled is key. I'd also add to incorporate strength training for your calf and ankle to help stabilize the tendon. It's a long process, but patience and consistency pay off.
I swear, everyone's always looking for a magic bullet. Have you tried 'Born to Run' by Christopher McDougall? It's not a traditional training manual, but it's got some great insights on running form and the science behind it. Worth a shot if you haven't read it already.
I used to have the same issue. What worked for me was to focus on my posture and cadence. Try to keep your head up, engage your core, and aim for a higher stride rate. It takes time and practice, but it's worth it. Don't be too hard on yourself if you don't get it right away.
Beating your own times is a solid goal, but if you're not seeing progress, maybe it's time to mix it up and try something new.
Same old snake oil, different packaging.