Hey Nova,
When you pulled the carb apart and re-built it, was there an O-ring on the top and bottom of the Air/Fuel Solenoid? There is supposed to be one at each end of this solenoid where it fits into the carb castings (bowl & lid).
My guess is that your missing a jet or maybe a check ball or something for this to be happening.
Is the truck an auto trans truck?.......was it an auto trans truck and maybe it was switched to a manual trans?
The reason I'm asking this is, the auto trans had a LOW PRESSURE electric fuel pump inside the gas tank, and a block-off plate on the head where the mechanical fuel pump is located......if it has the mech. fuel pump on the rear, passenger side on the head AND a electric pump in the tank, it's possible that the needle/seat won't close because of the extra fuel pressure.......just something to check maybe. If I remember correctly, the auto trans truck should have a fuel pump relay under the drivers side kick panel.....so you could look there maybe.
I am going to post some pics of a 1988 2.2 carb that I cleaned the rust debris out of (from a rusty fuel tank) and got it going again a couple of years ago, just so you can see if you remember if yours was missing anything in the float/fuel bowl area.
Maybe one of the pics might show if yours was missing something.......it's worth a shot anyway.
Wanna see the inside of the gas tank too?
OK!