Visit Suzhou upon getting to PVG

Direct long-distance buses from PVG to Suzhou are available. According to your timing, try to catch the schedule of 14:50, 15:20 or 16:10, and the whole trip would take about 3h. Or, you can take subway line 2 to Hongqiao Railway Station and take a high speed train to Suzhou. The second plan would save about half an hour.
For the return trip, a high speed train from Suzhou Railway Station to Shanghai is convenient. It would take around 30min.