pixelation on HD
checking your signal strength in the install menu would be a good clue regarding the quality of your reception. a solid installation would normally peg the potentiometer at around 100. from my experience anything under about 70-75 will lead to pixelation and loss of channels. many say that it should work with readings over 50 but no.
check the base of your dish support. over time, leverage on the base caused by the dish buffeting in the wind will loosen the lag bolts and it will cause the dish to fall off the signal. even a little bit of looseness will cause problems like you describe.
some times you can simply carefully tighten the lag bolts securing the mast and it will return to its optimized position, but often the installation of the mast base is poor and it would need to be redone. you might get away with some high quality glue in with the loosened lag bolts and then support the dish in such a way where it can cure in the right position. but more than likely you will need to find someone with a sat meter who is experienced in how to use it. then re set your base solid again, level the pipe head, optimize the hub so it is not loose and re aim the dish.
roof installations and concrete installations are notorious for coming loose at the base. eave installations are recommended by dish but often the wood in eaves is deteriorated or the whole eave is loose. trees are often 'shot through' but can lead to problems even if a 'good' signal is found. you can buy an inexpensive sat meter that is audio only then request a description on how to aim and optimize your dish.
if you are handy with tools and such you should be able to get away with not requesting a dish service call. if you are nice and a good negotiator you can probably get someone that is qualified to re peak your dish for a very reasonable price.