HELP - Poor quality picture but only on some channels on one TV

I am experiencing poor quality picture on some channels (42-53) on just one tv and cannot figure out why. If I switch to one of my modulated channels and view the same channel via a different source (e.g. my Tivo) the picture quality is great.


Since the picture quality is great on all other channels I have ruled out any cable quality issues.


I did my own wiring (all direct runs to the headend) using RG6 Quad and high quality Snap-N-Seal connectors.


The signal is basic CATV combined with the signal from my ChannelPlus modulator and is fine on 4 other TVs.


The tv with the problem is the longest run but only by about 20 feet.


Don't think I an under or over driving the signal to this location. It should be about 18db based on the amp/splitters/and cable lengths.


I don't have any "filters" in the system and use a couple of attenuators on the signal from the modulator to balance itbefore combining it with the CATV signal.


Any advice would be GREATLY appreciated,


bob