What are a few signs of fatigue and any other problems and can you get a rich problem from them both are set at 6.5 thanks
Regulaters don't normally fatigue. Some "lesser" brands and types will creep, and the pressure will rise, but that will show up on a gauge.
6.5 is not a problem un less your running .130 needles. They would have to be in excellent shape at that pressure. Even with .110 you need to be sure they are in good shape. Are you SURE your needles aren't allowing the bowls to over fill. Bad seats OR o-rings will allow the bowls to overill.
I am not a big fan of dual regulators. If you don't run a balance line between the 2 on the outlet side, its almost impossible to get them set the same and maintain it.