PSS Airbus Navigation Problem

[Airbus 14]

Hello:For some strange reason my PSS A320 is not following a flight plan correctly anymore. I have tried 2 AIRAC cycles and the results are the same. I first noticed the problem on a flight from LEMD to LEBB and further testing at my home airport on a flight from KBWI to KLGA confirmed the problem. The plan is KBWI PALEO3 ENO KORRY3 KLGA. After takeoff and the A/P engaged in managed flight the plane tracks to PALEO ok and then begins to drift west off its course to SPEAK. In fact the MCDU shows ENO as the next waypoint and the ND drops SPEAK completely because the plane never tracks directly to SPEAK! Although I never completed the flight, the plane never tracked directly to any ND displayed waypoint after PALEO. The plane rolls left and right randomly as if searching for the correct path, but it always seems to maintain an FMC brg west of the displayed ND track. For example, the FMC brg is 073 degrees but the ND displayed track is about 130 degrees. I tried doing a DIRECT routing to RBV to set up a T-P track and sure enough the plane turned to 150 degrees while the FMC brg was 087 degrees. Please help with any thoughts on what might be causing this problem and how to fix it.I also posted this problem in the Airbus Forum and hopefully someone here who is still flying the PSS Airbus might be able to help also. I know, I know you will say "Why don't you get an Airsimmer or Wilco airbus?" But my PSS A320 has always, up to now, worked flawlessly for me and it sure beats other airbus offerings.Thanks for your help!Airbus