Got the 'stang out of winter storage today and one of my problems from last year is still with me so I'm going to try & fix it. About every 5th time or so I go to crank the car the starter motor turns over incredibly slow, like its being held back by something. When it happens I may have to hold the key in the start position for 20 seconds or so just to keep it turning & hoping it might fire. Most of the time it turns over fast & fires right up. I don't think this is a battery related issue, it had a battery with a fresh charge in it. Any ideas?