Optimizing Home Internet for consistent upload speed

Hi everyone! I have been through hell trying to get the most consistent service using my new home internet setup.  I initially got the grey cylinder and through some troubleshooting / research / 20+ hours on the phone with fairly useless tech support via the Philipenes but have recently gotten a second line with the Arkadian model.  

I just set up the new device and am not getting anywhere near the speeds from the grey cylinder + a TP-link wifi router that seemed to boost the signal a good bit.  Do I need to get another router for this new device? Or a wifi booster? Or should I connect directly to the black box with a good ethernet cord? My job relies on very consistent and fast upload bitrate so ultimately that is the goal.  So far, I've tried everything except reaching out here so I figured it couldn't hurt to ask! 

Any/all advice would be very helpful! Thanks!!!