Slow speeds with new N600 WiFi Cable Modem Router

I have just purchased the N600 Wifi Cable Modem Router to replace my old Comcast Xfinity modem in hopes of recieving a better internet connection. I have a PC located about 30 feet away with only one wall in the way. With the Comcast modem I was able to get speeds around 30mpbs (Im suppose to be getting 150mpbs) pretty consistently. Now with the N600 I am only able to get about 5mpbs. Is this something that can be fixed with some setting changes or is the N600 not worth it?