Knothead--Can't say why you aren't catching fish on a Tellico nymph. It has long been one of my favorites and there's no telling how many trout I've caught on Tellico nymphs over the years. Yellow is a magic color whether in a Tellico or in other flies. Incidentally, were you aware of the fact that there are two streams with the name Tellico? The one you likely mean is in Tennessee. There's another one in Macon County in North Carolina.
Jim Casada