Starter? Problems

I have a 1994 Aerostar 6 cyl. with 110,000 miles. Occasionally it is reluctant to start. After several tries it catches and starts then starts fine for a period of time then is balky again. I had the battery tested and it was good. Last time I had make several tries with the gearshift in neutral and park. When it started it kicked up fine. Could it be the starter?
Peg French