Fuel Pressure Suddently drops

[DarrylFoster]

I'm hoping to get some additional ideas on what my issue could be. I have an RV-7A with an IO-360-M1B engine. Standard setup with a mechnical fuel pump backed up by an electric boost pump. Close to 600 hours on the engine.

When I climb to an altitude above 4500 feet (it's never happened below this altitude), after about 20 minutes, the fuel pressure will suddently drop. A few seconds with the boost pump brings it back up but I'm really stumped on the issue.
I've installed the cooling shroud with blast tube on the mechnical fuel pump and I've redirected the hot air from the heat muff exit tube away from the fuel pump. All exhaust pipes have a heat sheild next to the fuel lines. Fuel lines are fire sleeved.

As you can see on the below output, it is a real issue and not a false reading as the EGT's starting dropping as well.

 

[FredMagare]

If it was just a drop in fuel pressure, I'd imagine air in the line leading to the sender. However, your problem seems to effect all cylinders and so I might suspect a restriction in the fuel system (debris that is overcome by the electric fuel pump?) or possibly a leak after the electric fuel pump but before the flow divider. Just guessing but definitely an anomaly to identify before further flight....