Fuel pressure dropping.
 

A week or so my cars engine stumbled going up a slight hill.
It drove fine after that, once home I noticed my fuel pressure
Was low and about half of the 5.5 lbs I had set years ago.
I have a vented gauge and it has never done that before.

I have a small electric pump at the tank (Carter p72001) on a toggle
to assist starting after sitting.

I replaced the mechanical pump and it seemed fine until I got home
From my test drive.
The hood was up, The fuel pressure was about half what it should be,9the engine quit and I
Heard and Watched the gas sucked out of my clear gas filter back
Toward the tank.

I have a vented tank.
Could the free flow electric pump be partially obstructed?
Could a bad mech pump cause this?

Help!

Is the fuel pressure gauge one of the sealed types? If so those always read low when it is hot under the hood. You can drill a small hole at the top of the gauge housing to cure the change in reading when the under hood temperature is up.
Opps just read the rest of your post. You already have a vented gauge. I would check your vent at the gas tank.

Gauge is vented.
 

The gauge is vented.

I'm with Radman, check to see if the tank vent is obstructed.

Vent is clear.
 

Vent is clear.