New HP Great - 388mbps down, Dell 2 years young - 4.5mbps down 30mbps up - Cox No Suggestions

Hello everyone,

Problem is:  New HP Great - 388mbps down, Tablet Android 300mbps down Great, Dell 2 years young - 4.5mbps down 30mbps up Bad, Dell Desktop 8mbps down Bad.  Cox has no suggestions.  I updated Dell drivers, firmware, and even have Dell 2 year laptop directly connected via RJ45 direct connect to the Arriss TG1682G. This problem started a month or two ago.  Should I ask Cox on how to use the Arriss TG1682G as a bridge only, and reintroduce my own router?  So frustrating, appreciate anyone's help!!