Cabby, I'm not sure where you're located, but I'm 55+ miles out from the DC towers. Although WTTG-DT is broadcasting at full-power (1000kW), their DTV antenna is more than 200ft. lower than its competitors (WJLA-DT, WUSA-DT, WRC-DT). Additionally, their DTV antenna it is side-mounted and is located on the other side of the tower (good if you're in Winchester and points north - bad if you're down in Fredericksburg).
I get good reception from March through October, but reception for me is unreliable during the winter months due to their antenna configuration, my distance, and changes in tropospheric conditions. The good news is that WTTG-DT (FOX5) is raising their DTV antenna by July and WDCA-DT (UPN20) will be moving to their tower and going full-power...as mandated by the FCC.
Anyway, where are you located? How long have you experienced this drop in signal level? And do you still receive a reliable signal (i.e. don't break up, etc.)?