Multipath is the problem. Reduction of the strength of the Very Strong direct signals / reflected signals will likely help.
http://www.antennasdirect.com , has a variable attenuator. Repeated problems of reception complaintes with the computer connected tuners here at tvfool. Computer connected tuners like a Nice Clean signal. Connect the antenna direct to a tv with a built in Digital Broadcast Tv Tuner. Attics not the most friendly places for a tv antenna to be , move the antenna to above the roof.