Are you using latest firmware?

In future the firmware may suport 3G USB adapters?
I don't think so...TP-LINK Routers which support 3G USB adapters are TL-MR...

after around 12 hours or less of uptime the NAT is down, i can't download anymore with 23 MB/S only 11 MB/S,

Sounds like you are running bittorrent or other BT download. I want to say 11 MB/S is quite a speed...Maybe your ISP's Internet line is tried after long hours high-speed downloading. When you reboot the router the Internet connection is re-connected so that the full speed is re-gained

I think the 11MB/S is very fast. If my PC have this speed, it will hang because of the CPU and memory. If you get 23MB/S, I think your computer become slow.

My ISP can offer 94 MB/S with 1000 Mbps subscription with 15$ usd per month, me i have just 200 Mbps with 10$ per month and i am able to download with 22-23 MB/S i have Fiber and GPON.
It's not my ISP fault, it's the router, anyway... it's seems the problem gone... i hope... , now i have 1 day uptime and 4 hours and i am able to download with 23 MB/S

And i have the latest firrmware


And this router suport 3G USB Adapters with SuperWRT or OpenWRT but these firmwares don't have NAT support.

EDIT: Can some Moderator move this thread to Global and WDR3600? i don't know why it's at China.