challenge under 750 under AP mode

seek support here about AP mode. 

I really like the router mode of my 753 package. Now as I want to upgrade my router to 2.5G, I need use a new router to do the network dialing and DHCP and put my RBR750 as AP mode. Under the AP mode, the wifi speed is really slow and even under wired connection, my PC could only very slowly to access netgear admin page. 

Any suggestion will be highly appreciated for the AP mode.