@ScreenName1235 

Update: I just connected my TV directly with erhernet cable from modem and I am getting around 95mbps, so it looks like extender is NOT the issue. Maybe one of my cables from modem to extender is CAT5 and supports only up to 100mbps, not sure what else it could be. I checked the cable out of modem and its CAT5e and the cable going into extender is also CAT5e. They are two different cables, it looks like they were joined somewhere in the walls of the house I live in, so potentially there is a 3rd cable in there that was joined and it is CAT5 only. 

Anyone have any suggestions? Dont really feel like ripping walls apart. 

Update 2:

Connected the extender with 2 separate CAT5e and CAT6 cables that were 3 feet long directly to modem, and in both instances got 90mbps. Connected my PC with same 2 cables directly to modem and got 1gbps, so it can only be one thing: The extender ethernet port can only accept 100mbps in AP Mode, but specs say 1gbps. Am I doing something wrong?

  @ScreenName1235 

Hi,

Does your router/modem provide a way to indicate the current link speeds of the LAN ports? (either within its user interface or via small LEDs directly on the physical LAN ports)

The Ethernet port of the RE550 should support 1000 Mbps also in AP mode. My RE450 V4, which is based on the same hardware platform, certainly does.