So, it looks like Gaspar hit the nail on the head.
I removed the Air Trap and ran the main fuel tank directly into the shut-off valve then to the pump. On running the engine, the Pw dropped by half, to around 1300 compared to maxed out at around 2600 when pulling fuel from the Air Trap. It would hold 130,000rpm continuously.
This Air Trap has had 70 flights on it, and on did-assembly it had no sign of slime or anything unusual on the paper filter.
My second 140XBL also runs a MAP 40z Air Trap with no problems, but it has half the number of flights on it.
I did notice that the brass fittings had some significant shavings remaining on them which could cause line restrictions, although the filter would prevent them getting to the engine.
I have another MAP 4oz Air Trap on order.
I'm considering setting a Pump Voltage alarm in my Jeti DS-16 to indicate when the Pump Voltage is approaching the maximum (6V) as an alert to fuel restrictions. Normal ops is around 4V, so that should give plenty of headroom.
Paul