I don't see that happening in my Win 8.1 but then I have MSC v13.6 so really can't compare. Try running the Virtual Technician to see if it fixes anything: http://mvt.mcafee.com/
If no help then I suggest contacting Technical Support, it's free by phone or online chat and linked below.
Toronto ▪ Canada
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Before concluding that problem is with McAfee I would suggest you try the below
1. Turn OFF McAfee Firewall and check if Internet is faster.
2. Turn OFF Real Time Scanning and check if Internet is faster
If either of this result in slow Internet , Uninstall McAfee and see if Internet is fast.
Post back your observations for proceeding further..!