Gigabit Internet Speeds

I decided to up my internet speed from 300MG to 1GB. My speed was around 25MG up and realized I was paying for 150MG. So, decided to upgrade my modem. After connected, speed increased to +/- 100MG. After several hours on chat trying to figure out why I was not getting 900-1000MG, I decided to have a tech come out. Tech was very knowledgeable and thought my signal was to strong because the distance from cable box to the house was only 25 feet or so. After several speed tests, no change. Directly connected to the modem, I could get 125-250MG but was inconsistent. The Techs meter indicate all was good and it must be the modem. I exchange my new Netgear CM1000 to an Arris SB8200 thinking this would be more compatible based on Cox recommendations. After changing out and spending several more hours with the Cox chat, same results. Ugh..

It appears there is either a high resistance connection or possible EMF interference. The AC power is next to the main cable box and the box at the house is next to the AC Meter and the other side of the meter is my main house breakers. Since the house was built in 2011, you would think the cable would be shielded but I have not verified that.

My Question is....is there a way to test for AC EMF on the cable or verify cable resistance under a load? What are some other tests I or the Cox Tech can do?