@eparker6 - I'm a little late to join in this conversation. I was at Crater Lake enjoying the views and doing some hiking. I am 13 years post transplant (simultaneous liver and kidney). I am/ was in good health, too, with no underlying conditions except for the liver disease that took my kidneys, too. I used to walk for exercise. My husband and I enjoy hiking. Looking back, I remember that we took a trip to the Great Smokey Mountains National Park for hiking 9 months after my transplant. I found that I could hike but it was slower and not as far. I had very little endurance at that time. Over time my endurance has built up, but I now contend with some asthma and 'age'.
@myfablife indicated: Give yourself time and patience. I know you will be pleased.
As for medications, We transplant recipients do start at a higher dose, and it is adjusted as your body responds. Antirejection medications are a life long commitment.

@eparker6, Are you running for distance, time, or both?