89 S10 4.3 Need help troubleshooting TBI/IAC Idle issue

[76C10Stepside]

Hey, ChevyTech. Have not had time to work on the S10 yet. I disconnected the fuel line at the fuel filter, plugged off the side of the line that runs to the tank, and ran the side that runs to the engine into a 1-1/2 gallon gas can. A couple of days later, the can was FULL and overflowing. I emptied it into another can, and now it has another gallon of gas in it! It's a constant very slow dribble.
Where is all this gas coming from??? I don't get it!

If I understand the fuel delivery/return system on this truck (thought I did), there is a hard line to the TBI/regulator, and a return line for returning any extra gas to the tank. Where would 2/1-/2 gallons of gas come from???

Besides being totally confused about this, I am concerned that when I loosen the screws for the fuel meter cover, gas is going to spray all over the place. Also, I'm wondering if I should test the fuel pressure per your directions (using a tee, a correct guage and with engine running) BEFORE I take it apart, OR take it apart and try to identify what it leaking and replace parts as needed first?

I get the feeling there is too much pressure built up inside or something...