Cox Ultimate Internet Speeds Extremely Slow

Last Friday I upgraded from Cox Preferred internet (Speeds up to 50Mbps) to Cox Ultimate (Speeds up to 150Mbps). I was using a Motorola Surfboard Model SB6121 modem and was getting consistent speeds in the mid to high 40's Mbps.  I upgraded my telephone to digital too which required a new modem.  The Cox technician gave me a Ubee model DVW326B modem for the telephone and internet services.  After the technician left I ran some speed tests (Cox Speed Test and Speedtest.net) and found that I was only getting 20-30Mbps consistently with some spikes hitting just under 80Mbps.  After running the speed tests throughout the weekend with the same results, I called Cox tech support.  They scheduled a tech to come out today (Wednesday).  The tech came out and miraculously the speeds were in the 100-130Mbps range.  He told me that all he did was replace a splitter, barrel connector and determine there was no noise in the line.  I will add that the tech said there was nothing wrong the splitter or barrel connector it's just something he does on all his calls. He was here for about an hour and ran the same speed tests I listed above and the results were all over the board. He also called Cox and had them reset the modem.  Prior to him leaving the speeds seemed to be consistently near or over 100Mbps.  I told him that I was not happy with that because it was still not what I was paying for.  He said that he would schedule a tech to come back out in a week to retest the speeds again but I was to call Cox if I had any problems before that.  Well, 30 min after he left my speeds were back down in the 20Mbps range and have been there now for over 4 hours.  I called Cox and after being on the phone for 30 minutes found out that I have to wait until Saturday for a tech to come back out.  

My computer is connected to the modem by a cable not on wifi.