You most likely have limited reception where you are. And with summer coming it may get worse from noon till late evening due to increased solar interference. Digital is more affected than analogue when it comes to distance, reflection and natural electromagnetic clutter. With analogue the signal fades unlike digital that just drops off. A higher FEC can help a digital stream adapt but has the result of wasting bits which could have been used in the compressed video stream.
You could try a higher mounted or longer antenna. The only other idea is to use the tax payer funded satellite service.