I used McAfee Internet Security for a long time because it came free with my internet service. But with each new "upgrade" my computer started running slower and slower, and CPU usage jumped through the roof. I switched to Zone Alarm and now my computer hums along just fine.
I still use McAfee Site Advisor for browsing protection. That doesn't cause any problems.
But that brings me to a caution. McAfee makes multiple products which may be on your machine. Do you know whether it is McAfee anti-virus, firewall, or Site Advisor which is causing your problem?