Steroids are known to increase blood pressure. Winstrol does not aromatize into estrogen so your problems are not estrogen related. I suspect it's a sodium issue.
Watch your sodium intake (don't eliminate it completely) and make sure to drink enough water each day.
Garlic, Potassium, Coenzyme Q10 (CoQ10), Magnesium, Vitamin E and Iron will all slightly reduce blood pressure as well. Look into a good overall detox/blood pressure regulating supplement like n2guard from n2bm.com.
Keep a close eye on your blood pressure. If it doesn't start to go down - go to your doctor and get him to write you a prescription for a blood pressuremedication. Don't take this lightly. Blood pressure is a silent killer.