How have you tried to do your testing. Can you have a receiver and TV at the dish with new wiring (coax) have you tried another LNB. It sounds as though the mast or mount may be out of alignment or not plumb, or the elevation of the dish may have changed. I know this may sound redundant, but if the receiver is good and the dish is good and the LNB is good it must be alignment.
When you find the cure please let us know it may help someone else.
Be patient and good luck.
Two Mercury II's, DG-240, 90cm Fortec, QPH-031, Viewsat Ultra VS2000, Solomend and an Openbox S9, DN Turbo HD dish w/DSS-LNB
I like to shop at Sadoun Satellite sales.