What else could be the issue with my adsb?

[483RV]

RV-7A with an Advanced panel -2 AFS 5600, Garmin GTN650.
Transponder is SV-XPNDR-261, ADSB module is the 470 and GPS signal is configured from GTN-650 to feed the system.
My adsb is intermittent at best. Flightaware only shows me for very short sections of each flight. I have never been able to generate a PAPR for any flight - always says that it is not found. Traffic shows on my screens but disappears and reappears intermittently. I have several times had shadowing where I receive a traffic annunciation warning that there is another plane exactly where I am and at my altitude - but there is no other plane - it's just me. In Class B after takeoff, I was initially not able to be seen via adsb but they had my mode S readings. Eventually my adsb out showed up for the Class B controller but not right after takeoff and not consistently.

What I have tried:
Antenna placement - it is too intermittent for gear leg shadowing to explain all the failures and a PAPR would generate for at least part of the flight which it never does.
GPS signal - I did troubleshooting with Jonathan by phone to ensure that the menus on my GTN 650 and the AFS screens were all set correctly, and they all are without fixing the problems.
Flying in lots of places - I was concerned that antenna placement in my area may be sparse so I have tried it out in every area around me within a 2-hour flight time - no fix.

So - what could be my issue? I don't feel I have reliable enough signal to transit Class B and I need to be able to do that along with not trusting that my traffic display is actually showing me all the available traffic.
All I can come up with is that I need to replace my 470 adsb box with a 472 - but I don't want to spend that money and still end up without a solution. Does anyone have any ideas of what else I should be trying. I am glad to buy and replace anything to solve the issue but I can't figure out where to even start to get a solution. Thanks for any suggestions you might have.
Tim

[483RV]

I forgot to mention that several times I have seen a yellow pop-up warning on my AFS screens that says "No ADSB Pos"
The warning has only stayed on for about 10 seconds and then disappears on its own and does not repeat that flight. This has happened about 5 times in the last 6 months. It is usually shortly after takeoff or even while I am still on the ground.
Maybe that is helpful diagnostically?
Tim

[Jonathon]

Replacing the ADSB 470 with a 472 will improve your weather and traffic picture, but it will do nothing for the stated problems which are related to your ADSB out. The preponderance of evidence suggests that the GPS position from your GTN 650 is not getting to the transponder. This could be configuration or it could be wiring. Since it seems we have already gone through the settings, the next thing that you need to check is that the serial port wired out from the GTN is making it to pin 3 on the transponder, with specifically 1.21k ohms resistance provided via an external in-line resistor which must be added to the wire.