I've never heard of that happening before. Go into Firewall settings and make sure that browsers are all given full access.
Double-click the taskbar icon to open SecurityCenter
Click Web and Email Protection
Click Internet Connnections for Programs
Hint: Click the word Program at top of the list to arrange them alphabetically
Go down the list and make sure Internet Explorer and any other browsers you use are all given full access
Click Edit to change them if necessary and Save any changes.
I'm assuming that you have no other security software installed that could compete with McAfee and that you haven't forced Windows Firewall to remain on alongside McAfee as that could spell trouble.
Other than that I would contact Technical Support directly. It's free via phone or online chat and available through Useful Links at the top of this page.
They are best equipped to troubleshoot these things.
The only time I've heard reference to Internet Throttling is in regards to the doubtful practices of certain Internet Service Providers restricting trafiic at peak periods especially, mine included unfortunately.