Router Speed is Significantly Reduced

Hi there, I realize this is a similar thread to many others, however, I haven't been able to find a solution to my issue:

 

Model: WNR2000v3

Cable: Optimum 200 (200 DL / 35 UL)

 Firmware: I've updated it to the latest version

Other equipment: I sometimes have a Netgear range extender connected, but that signal is very strong, receiving up to 170 Mbps (not actual internet, just the connection).

 

Wifi speeds coming out of the router seem to cap at 45 Mbps (sometime as low as 5Mbps), wired speeds at 60 Mbps (often lower). 

 

Connecting directly to the modem yields up to 200 Mbps. 

 

Mode on the router has been set up to 300 Mbps. 

 

Can anyone advise why the router seems to be throttling these connections? I realize this is an older model, but it seems to be in fine working condition otherwise. Thanks!