Gerard,
<<...the fuel pressure normally sits at 2 psi, just above redline in the cruise, but intermittently (and apparently spontaneously) wanders to 5psi before returning to 2 psi.>>

I have noticed the same thing.  A former Piper rep. told me that Piper tried to figure out what causes this behavior many years ago.  Despite all the instrumentation they installed, they never could find the cause.  They left the matter as an unexplained but harmless quirk.
The true redline for the engine is 0.5 psi.  It is quite normal for pressures to indicate lower while at high fuel flow rates, such as during take-off, and highest at low/no flow.  I don't recall seeing anything lower than 2 psi in my plane.  Less than 2psi would bother me if this was a change from typical observation. Questions:   Was this the first time the pressure has dropped below 2 psi?  Have you checked all of your filters and strainers recently?  Have you checked the flow rate of the electric pump at the inlet to the carb.  You might also want to check the calibration of the gauge.  I have seen aircraft gauges out of calibration right out of the box and others that drifted over time.  Other items that may be relevant:  Are your two pumps in series or parallel?  Do you have a fuel flow transducer in the line?

Chris Zavatson
N91CZ
360 std
www.N91CZ.com