Gigablast Speed Inconsistency/Upstream Channel

1. Hardwired directly to modem (SB8200), only received up to 400mbs consistently, spoke with Cox, they suggested replacing the modem.

2. Replaced modem (CM8200), Out of 15 test, only once got over 700mbs, spoke with Cox, they sent a technician out (3rd party).

3. Technician arrives, all signal levels are good, his meter reads +700mbs, show him what I was experiencing with 2 different devices hardwired directly into the modem, says "That's weird" and leaves. Noticed upstream channel was a green light only (not doc 3.1), he didn't have any idea.

4. Spoke to Cox again, says the CM8200 is not supported, purchased a brand new CM8200, same result - speeds are still around 400mbs.

Anyone have any ideas?

Does Cox support Doc 3.1 upstream? 

Thank you.