How about give a try to turn off the Hardware NAT on the router?

Disable NAT, not a solution, because when NAT is OFF, port forwarding not working!

This device, in fact, is unusable for me, reading this forum, I understand that and to other users, the situation is identical. Apparently there is global problem with the software .... We are waiting for decision.

There are two NAT on the TP-LINK menu.One is software NAT, another is Hardware NAT. Disable Hardware NAT will not effect the port forwarding function or any other NAT function

I Disable Hardware NAT, but now, all my peers connect very slowly (behind router have server with about 80 peers). In fact, even when Hardware NAT is enable, peers connect slower than with my old router, which had only 200 MHz CPU. My server makes a high number of TCP connections, but uses very little internet speed, about 2 megabits.

Example:
Upon reboot the server behind the old router, all peers are connected after 20-30 seconds. Now with the new drives, the same process takes 5-6 minutes.

Perhaps there is an additional setting for the high number of TCP connections, which I'm missing?

http://forum.tp-link.com/showthread.php?2395-Problems-of-WDR-4900&region=china I just found this post and you can try to install the Beta firmware to give a try.

A few days ago, I installed: wdr4900nv1_en_3_14_1_up (130304) _beta.bin, now is not interrupted, but my peers, still connect very slowly.

wdr4900nv1_en_3_14_3_up_boot(130320).bin
here : http://everbest.ftpserver.biz/TP-Link/FW/wdr4900nv1_en_3_14_3_up_boot(130320).bin