Read and understand this about Real Digital Tv Channels and Virtual Digital Tv Channels ,
http://forum.tvfool.com/showthread.php?t=695. The digital channels at the top of the list are Strong and should be booming in not wimping in. Might be a bad Digital to Analog converter box . If New RG-6 coax from the Antenna DIRECTLY to the Converter Box , by passing every thing else. And a New coax from the converter box to the Tv by passing Every Thing between the converter box and the Tv and the antenna is pointed in the correct direction does not produce strong channels then somethings fishy here. I am narrowing my eyes. This does Not pass the smell test.