Depends on your age,
above 50 to 60 years old, systolic blood pressure is associated with higher morbidity.
younger individuals are more at risk for elevated blood pressure.
However, a low diastolic with a normal or elevated systolic blood pressure is not a good thing as pulse pressure (SBP-DBP) is also a associated with higher morbidity.
There is theoretical logic behing both systolic and diastolic bp to be risk factors. Mean arterial pressure is usually (grossly) measured as 1/3 SBP + 2/3, therefore DBP where DBP represents the majority of the pressure on the vascular wall. On the other hand, SBP while shorter can be much higher generating higher quantities of sheer stress on the vascular wall.
As for the OP's symptoms, Anabolic-Androgenic Steroids can cause dyspnea through a variety of mechanism.
On the top of my head I would say,
Elevated hematocrit (secondary to increased RBC formation by AAS) which increases blood viscosity which increases the work of the heart to maintain blood flow.
Myocardial infarct or pulmonary embolism secondary to increased viscosity/activation of coagulation pathways by AAS
Dilated cardiomyopathy secondary to elevated BP (2 to increased hematocrit and increased heart remoddeling by AAS) or myocarditis
There probably are other causes but they don't spring to my mind right now.
Hope this helps,