pmrnew, PMR can increase the intensity of heartbeats and increase blood pressure because of stiffening in arterial walls. Prednisone, too, can increase both symptoms. I suspect that your body is responding to the prednisone. You could get a cardiologist involved with the prednisone dosage. Your symptoms are often consequences of prednisone dosage changes.
Prednisone increases the body's sensitivity to adrenalin acting a bit like cortisol. It also causes fluid and salt retention increasing fluid levels in the vascular system making you feel those beats.
I like your conclusion best--your body is complaining about the new, healthy lifestyle and is increasing the volume because you seem not to pay attention.