|From the looks of it, you've got everything configured correctly so I can't think of what may be causing your issue...........especially since you've replaced the router with a newer one.|
But wireless connectivity to the internet is poor.
You do understand that wireless is inherently subject to lag and latency issues which could easily cuase poor connectivity? This may be nothing more than a simple case of wireless being wireless.
Ping to the main router shows most packets are lost.
I'm guessing you're pinging from a wireless client. If so, try the same from a wired client. Do both at the same time (if possible) and use the /t switch with your ping (it makes the ping continuous) and let it run for a minute or two and then stop it (using Ctrl-C) and check the stats on 'packets sent' versus 'packets lost' on both and report back.
If you only lose packets on the wireless client, it's the client, the client's NIC, or just the normal wireless issues.
Remember, wireless is never as fast, or as reliable as a wired connection. And, it never will be.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.