It is very important that your son be monitored VERY closely. I wouldn't let him out of my sight with others. If you have to keep him in some sort of child care facility, let the director know the nature of this problem. They will be sore to monitor him closely.
This may sound paranoid, but it is a way to keep him and others safe until this passes. You might also listen closely to his conversations. If he does or says anything inappropriate, you might warn him and then if it happens again, end the playdate or isolate him, etc.
He is at the age that neurofeedback might be helpful. We have done this with a local neuropsychologist. He was very thorough (more so than any therapist or doctor). This therapy helps the child learn to control these impulses.
Good luck and God bless
Contact Safer Society in VT or STOP IT NOW both of which can refer you to specialists in this area of practice. Your son could benefit from specialized assessment and treatment, as well as close supervision. There may be medications that can help him, too. His behavior is alerting you to the fact that he has an ongoing problem that has yet to be addressed. Don't stop until you find someone who understands his problem and can help him. He also might benefit from comprehensive psychological testing to help understand the underlying nature of his problems. Good luck.