Further tips: Get a faster router; get a new ISP as suggested (AT&T's equipment really lags behind on technology), and then replace your desktop PC with built-in N adapter. AT&T didn't tell you about the newer N-class router, as the training of their Customer support reps has severely deteriorated over the years. That's a 2-ended failure of AT&T; lag of technology premises equipment, and lack of internal training. Very few people stay with them longer than 1 year these days; at least in my part of the country-West Coast.
As far as router brands go--there are only 3 brands: Cisco, Cisco/Linksys, Netgear to buy. Anything else will produce many kinds of network problems I won't go into here. Needless to say all of those...