Hello Prasanna, how are you? Have you rules of outbound in your Palo Alto Firewall? Can be filters rules reading each outbound packages making slow upload traffic.
Is there a reason why your tcp-mss is so low?. I beleive that Cisco recommend 1300, maybe tweaking this on a test AP and adjusting it. I've seen issues on wave 2 AP regarding tcp-mss but only when it's not set going through firewalls and specifically on client intel chipsets.
