CGM4140COM Ethernet port speed slower than WIFI

I have a CGM4140COM modem/router and I am trying to setup a point to point for a new building.  I am experiencing the internet signal dropping out.  After some investigation it appears that I am only getting <100mbps out of the Ethernet ports.  I am paying for 800mbps getting about 500mbps on WIFI.  After reading some on this forum, I see that some ports do not have gigibit capability to support higher speeds.  However, this modem/router is supposed to be gigibit capable.  So what is limiting the speed?

I am using CAT6 cables and yes swapped them to check cables.  I cannot get more than 90mbps.  I am at a loss as to what the next steps are.  I would go buy a new modem/router if I thought that was the solution but I am leery to do so without some guidance that that resolves this issue.