Of course not, that would have been smart and totally narrowed the problem down
Well thanks very much, you seemed to have nailed it. I'm not sure why I didn't question the internal tuner TV in the den...maybe because it's a nicer set. Anyway I even split the line at the wall and am watching both sets at the same time. The tuner from the short run isn't perfect but it's still much better.
So, clearly the tuner is to blame. I'm just not sure what's wrong with it? Maybe it's being overloaded too easily? Or maybe it's just crummy? It's a Samsung HPS4253X. The other TV is a cheap Sharp LCD (albeit newer than the Samsung.)
So I should just get a standalone tuner?