You have a separate Wi-Fi router (Mentioned Linksys WRT1900?) which would be your Linksys WIFI and then you have a Motorola modem. The Modem receives the data, than the LINKSYS Router WIFi lets the data be assessable...
The 16 channels DOWN/ 4 CHAN Up are the CABLE STREAM connections from the MODEM to SERVERS, NOT the MODEM to ROUTER.. You would need two LOG INTO the LINKYSYS (links above) and make sure all settings are correct.. Also for verification purposes, eliminate the Linksys router altogether, direct connect the cable modem via ethernet into your computer and then run another test, you should have near you paid for advertise speed under direct ethernet connection.