I'm surprised you can get those two stations at all, given the negative NM values. I ran a report at 50 ft just for grins, using only your zip code, and NM values went up hugely.
http://www.tvfool.com/?option=com_wr...5b9475c5c88b89 You might want to rerun it using the map function, sliding the antenna icon around to a location right on your house (the actual location won't show up on the report, so privacy is preserved), as your original is only resolved to block level.
http://www.tvfool.com/?option=com_wrapper&Itemid=90
Try some different elevations, as given the gentle curvature of the terrain there (from what I can tell), it's likely that some extra elevation could make enough different to clean up reception.
You said you have an amplifier, but is it the exact model GUM recommended? Small things can make a big difference when trying to receive very weak signals.
Windy days are not the best for testing. My signals come in at 100%, from only 12 miles away, but with high winds, sometimes I get breakups and pixilation anyway.