G34 slow ethernet connection

I have dealt with Arris Cust Svc 4x and have had Sparklight Techs out 3X to figure out why I cannot get more than about 250mbs download speeds through ethernet connection.  I have a 600 mbs plan and should be getting very close to that via ethernet.  Sparklight checked the incoming signal to the router and it came up 950mbs.  Throughput from the router registered in the low 300s.

Sparklight says it’s a router problem, Arris says the upload power is too low, currently at 41.  Sparklight says they do not run the power any higher than that in their system and says that the power difference is not creating the low speed through put.  Arris says it does.  Sparklight will not change the power settings.  

Arris had me change the WiFi channels to lesser used channels saying that it could make a difference even with Ethernet speeds?  What????  So I did a factory reset, changed channels and everything else exactly as they said, waited 24 hours, did a power cycle…..no joy….same issue.

I’ve had this router 2.5 months….I want a new/different router…..

Thoughts??