What are your reception numbers? Go to menu, setup and look at signal strength. Anythihing below 75 will return marginal picture quality. Changing coax cable can be easy or a horrible experience depending on how the cables were routed. Length is not your issue. All the connections could be. As for what to use? RG-6 or better. Cable and connectors can be bought lots of places, but dont cheep out. Buy the best quality you can afford. Get rid of all the connections, try to run a single coax directly from the dish to the back of the receiver.