Simply Switched from Netgear C6300 to C7800 - Extremely Low WiFi????

so.... i had been using a Netgear C6300 for a few years, with no issues on wifi range at my house. 

I bought the Netgear C7800, along with upgrading my internet package with Cox last weekend.

simply disconected the C6300, and connected the C7800, same location.

Went through the install with Cox, and the ethernet line is fantasic!!! 900gbs+

however, the wifi signal has very little strength. it won't reach beyond 15 feet. even when the receiving devices (iMac/iPhones/Ipads) are in the same room, a few feet away, the RSSI is -90+, with a speed of 20-30gbs.

tried moving the C7800, the antennias, the channels.

what is happening? i would have thought it was a simple plug and play switch?