Are there any trees in the signal path?
If you have the problem with CH 38 when your antenna is aimed at 62° magnetic, and you don't have trouble with 40 or 46, I suspect tuner overload even though the antenna is in the attic. Try some attenuation like adding a splitter or two in the coax. A 2-way splitter gives 3.5 dB, a 4-way gives 7 dB attenuation.
Interpreting Noise Margin in the TV Fool Report
http://www.aa6g.org/DTV/Reception/tvfool_nm.html