Not getting gigablast speeds

I recently updated to gigablast speeds and none of my devices are pulling over 300mbps speeds when testing with multiple platforms. This includes both wired connections and wifi. My speeds can also range from as low as 56mbps and are not consistent. I am using a desktop with a confirmed gigabit ethernet connection. Cox recently sent out a technician that stated he was able to pull up to 940mbps on his handheld tester at the gateway, note I am still using supplied TechniColor gateway as I do not want to purchase my own equipment until I can confirm the availability of gigablast speeds. My service is still being provided over coax, as fiber is not in my area yet. Any advice  would be appreciated.