[ChevyTech]

The fuel pressure regulator is in the TBI unit and testing the pressure must be done with the gauge installed on a T fitting, engine running.

You are just guessing at the pressure because your gauge does not go that high, but 18 PSI is easily reached with a good strong pump when the gauge is on the end of the line, or the return line flow is stopped.

My guess is there is no problem in the tank. If the hose in the tank was split it would not hold pressure after the pump stops. The test you did does not show that the pump is good for sure, but the test leads me to believe the pump is good. You were in the TBI unit already so you would have seen if the fuel regulator spring is broken.

On ODB1 system and these TBU trucks it is a process of elimination, especially working over the internet when I am note using my senses to see how it is running. So far we have not definitively ruled out much.

I suggest you change the oil and get truck on the road to give it some run time after the changes you have made, so it can relearn the IAC position and fuel tables. This will also give it a chance to clean up soot off sparks plugs and the oxygen sensor.