under 100mb for "gigabyte" service while wired

Thanks for the replies.

To answer the question from EG:  The Technicolor CGM4981COM is a high-performance, white, tri-band Wi-Fi 6 (802.11ax) gateway used by Xfinity (Comcast), commonly referred to as the xFi Gateway XB8-T. It acts as both a modem (receiving the internet connection) and a router, supporting fast Wi-Fi speeds, 32x8 channel bonding, and DOCSIS 3.1 technology. 

It's what came with the service at no charge and it looks to be brand new, just picked it up for Xfinity store.

I do have cat6 on hand.. thanks for the tip.

Before I get help through xnfinity I thought I would try here to try something first.  What I have done is purchased a new section of cable that will connect where the service starts at my house.  This is because the current section has a kink and a tear in the plastic.   I doubt this is the issue, but decided to replace it anyway and new heavy duty one made by Monster cables (well respected brand) is on the way.  It's 100' section.  As soon as it gets here I will test again and open a ticket if needed.   Once issue is resolved I will post back with details.

Thanks for the support. 

Have you tested the speeds via WiFi?  Use 5gHz band while close to the XB8.  Clearly you SHOULD have higher speed via wired internet, however this could eliminate the notion of the Cat 5 being an issue.  It sounds like the cable you are in the process of replacing is the coax from your demarcation point to the XB8 location which should be RG-6 coax.  A defect here could give you issues which could be detected by looking at signal levels and signal to noise ratios. I would recommend keeping this cable as short as possible without other splitters if they are not needed. There is always the possibility that this is totally an Xfinity issue of provisioning and nothing is wrong at the premise. 

Tested by plugging into the port with the red line: 82mbs download 29.21 upload.

I don't have a way to check wifi right now as all my PC's have networking ports but no wifi.

Thanks

@user_k2odiz​ note Cat 5 is only certified for 100mbps, and at 100’ that is definitely pushing any ability to “sneak in” higher speeds as there is a lot of crosstalk that will occur over the run.  Cat5e and higher will have physical differences that allowed them to be certified for 1Gb+ speeds.  Hopefully your new cable is outdoor rated if you are running outdoors, as UV can destroy standard ethernet cables pretty quickly.  For longer runs, fiber optic is definitely better, but you would probably need media converters if your existing equipment doesn’t have SFP/SFP+ ports.