Premier Tier running at Preferred - not a legacy issue

I subscribed to cox on 5/25 and have been very frustrated with my speeds. I am paying for premier level service and I was told I should be able to expect an average download speed of 40 Mbps, and I have not been able to get speeds greater than 30 and averaging about 25, today it was 19 Mbps. I have chatted with tech support who restarted my services and this did not help. The tech who installed my services said that my modem Motorola SurfBoard SB6141 DOCSIS 3.0 Cable Modem would not cause this issue and even he was only about to get speeds of about 30 Mbps when he checked it. I am using a router but the speed checks have been done through both just the modem and through the router. The chat tech support has not been helpful and I am getting read to cancel my service if this can't be resolved.