Poor coverage after upgrade

Upgraded from Essential 50 (which was working fine for our 3,000 sq/ft home with devices on 3 levels) to Preferred 150.  Since the upgrade, we get zero coverage upstairs and the basement frequently disconnects.  The mid floor where the router/modem is also occasionally disconnects.  Speed is better, but coverage is awful.  Advice?  

Is the Cox router/modem not strong enough for my home?  

Can I have Preferred 150 with my own equipment (hate paying for a rental...my old stuff worked well)