Hello Everyone! I recently upgraded the avionics on a 1979 PA28-181 with dual G5s / GMA 342 / GNX 375 / GNS 255. Everything was fine until a day after a month and a half of the upgrade, when I started to get a fail in the heading data in the PFD G5, followed by a message "Not receiving ARINC 429 data" in the lower G5 HSI. I went back to the avionics company with the issue and they have tried different fixes like cleaning the connections, they changed the GMU, reseted the entire system.. all about 4 different times, but it just comes back. Today they said everything is fine, they think it might be the vibration of the propeller, might be out of balance.... but im not convinced about that. I am really frustrated about this, if anybody can give me a hint of what the problem would be and a possible solution, it would be GREATLY APPRECIATED.... Thank you in advanced!