Since you don't mention anything you may have checked on your own, or how many miles are on the vehicle, I'd say start with the basics. Check fluid level, perhaps have the transmission serviced. Fluid and filter change. Go from there.
sorry, I should've disclosed what's been done. I had the transmission flushed and filter replaced. The fluid is a little on the full side since I put a bottle of tranny shudder repair in there too. Thank you