Intel 4965AGN mini, connection problem to high speed.

Hi, I have a Dell Precision M6300 with a Intel 4965AGN mini card. I have no problems connecting to a 2.4 mhz and recievive a 144mpbs connection. My problem is getting connected to 5.2ghtz high speed connection. I am using a dual band wireless router, ASUS RT - N53 r and have attempted many settings and still can not get a high speed connection.

Thanks for what ever help.

Hdpartman