There's too much here for me to conjecture, and I'm not a medical professional, but a few questions:
Discomfort in breathing, how so? And the difficulty in hard exercise, what is the nature of the difficulty? Why did you feel that the pain was in your heart, I could understand your chest, and you were just exercising, any correlation there?
You provided a detailed post, but I'm curious, what did the doctor say to these questions:
What did the doctor say about the elevated Troponin levels?
They did "other tests" which were normal. Other Troponin tests, what were the other tests?
What did the various doctors you saw suggest may be causing the pain.
Did they try Nitroglycerin? If so, any changes in the pain.
Did they give you anything for the pain, either pain meds or cardiac meds?
Palpitations are quite often, how often. I get thousands of PVCs on my bad days, are you talking this many, and if so where they captured on the Holter and other tests, and do they occur or get worse on exertion? What did the Doc say about them? What did the Doc say about the elevated pulse?
Fortunately you had so many tests that you have good reason to feel reassured about your heart.