Pathetic download speeds via extender

Hello, I am using WN3000RP  in combination with in combination with my Netgear DGN2200v4 router. This router as you must be aware of supports both ADSL and Ethernet WAN. When I connect this router to ADSL and my Extender is connected to it, I get full speeds (8 Mbps). However if I connect it via Ethernet using Port 4 as WAN, I get horrible HORRIBLE speeds when I am connected to Extender. My internet speed is 100 Mbps and my laptop manages to pick speeds of around 50-60 Mbps on wireless directly from the router on the same spot where the extender is plugged in, however, the extender at MAX gives me 5 Mbps speed.

  OS used: Windows, Android, iOS

Requesting your valuable help in this.

Thanks in Advance