GRT Avionics

Ditto on that happening to me also on my Sport SX unit, really gets my blood pressure up until I figure out it is me!

You also can go into the GRT settings and specify that traffic only plus or minus such and such altitude will be displayed. I use +/- 1500 feet, so I don't get bogged down by traffic 5000 feet above me (who cares).

I don't know if the Sport does this, but the HX displays traffic on the PFD as well ...

What GRT EFIS are you using? The HX or HXr should have showed the close-in traffic on the PFD display, over top of the AI.
Just a reminder: unless you are in class A or B airspace ATC is not responsible for traffic separation. And, until 2020, there are no guarantees with ADSB, either.

I have the ...

Long story short, flying along at 8500' under ATC control. Have 2 targets showing in my area overlapping each other (Nav Worx unit). Display on one shows several thousand feet below me, covering up the other target. Then that target drops off showing the underlying target at my exact altitude. I ...

I think this is more of an issue low and slow. At my airport there are parallel runways so when in the pattern with another airplane the airspeed tape does not show Vfe, etc. A possible safety issue in my opinion.