why overheating and stalling

Hello, the first concern: sealant doesn't help. It can really cause problems, but I can't recall a time I've ever seen sealant work. Second concern: stop driving the car. You're causing more damage, and if you'd have made repairs at the onset of initial symptoms, you might have avoided different additional problems. You'll need professional assistance to first assess the cooling system leaks, then assess the overheating. They may be related, but indeed may be separate concerns. So many possibilities here. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops