My new KDF-E42A10

Just got my comcast hi-def box today and hooked it up via video 5 input. Ran optical cable to my receiver for sound. My question is I thought every hi def channel would look amazing. Most channels look great, example (discovery,inhd2) but some channels get really blurry during action scenes. I have the cable box set at 1080i. Same as the input for tv. Should I have it set differently? Also have dvd player hooked to video 4 input and can say I thought picture would look better than it does. I'm using component cables for both box and dvd player. I noticed that when running at 1080i it disables the drc pallete controls on the wega gate. This kind of sucks but, what can I do? Am i expecting too much from this T.V.? It was in my price range and i read good things about it. I'm using decent quality cables. Would buying a HDMI cable for the cable box make it better? Any help or info appreciated.