Interesting, see what your old setup box gets on TV vs new, to me it looks like a possible local overload (on some tv tuners, signal actually shows a drop even tho it is high) from the chn 36 with reflections being stronger.

The tv set I have is the Vizio too, it is one of the better ones but still limited in the setup showing only rf signal strength, multi-path acceptable but not as good as my set top ZD500.

Best omparison, your set top and the Panasonic side by side, same cable lenth, antenna etc.

Another option try a different antena with a bit more directivity.

Good luck and have fun with it!