Wolfshadw :
Gradually losing channels would probably tell me that obstructions are now present that weren't there two years ago.
I'd probably start with Antennaweb.org and see what channels you should be getting. Are the channels you've lost still listed for your zip code?
-Wolf sends
P.S. No need to enter your actual address. Just enter a zip code and then move the blue/white location dot close to your actual location on the map.
I've verified from neighbors that the channels have stayed the same.
What would the obstruction consist of ...exterior trees and that sort of thing?