I bought an Arris SB6183 modem and TP-Link Archer C7 Wifi router since the TWC provided unit was useless. Tech came out 6 weeks after initial installation, found original installer did not run new line. They completed the re-install and for almost 3 weeks speeds were great. This week, the speeds have dropped considerably. When I contacted them, they ran diagnostics, changed some router settings, then disappeared. No improvement to Wifi speed, and no follow-up after diagnostics. Are there any guidelines that I can use to help get my Wifi speeds back to acceptable levels?