There's no point in calling AT&T as your connection is OK, the problem is somewhere in your configuration. To be frank, you really shouldn't be trying to use the 'net at all with a machine which doesn't have effective anti virus, malware protection and firewall - are you saying they aren't installed, or that you simply haven't done a manual sweep?
Can you explain what you mean by the connection being slow, how have you attempted to measure that? Do you understand the term MTU?