Fuel regulator is hanging open/closed or the return line is plugged or kinked. Fuel pressure, can be tested somewhere between the filter and TB inlet. Above say 13 PSI or below 9 PSI and there is generally a problem.
The pump runs between 2 and 20 seconds when the ignition is turned on, any longer than 20 seconds and your probably, pushing to much fuel somewhere.
These trouble checks are for the 5.7, but I´m quessing applicable to your 4.3 also.
I´m guessing a injector/adomizer nozzle could be hanging open, a tip off, is when you turn the key (ignition) off and the motor continues to run for a few seconds (diesels).
Gas cap vent plugged. Charcoal/vapor canister valves, plugged/stuck, check the canister to see if it´s full of fuel. If it´s full of liguid, it will push/suck, raw fuel into the throttle body.
I remember something about the air cleaner housing/seal and gaskets, causing the vapor canister to collect liquid gas and cause problems.
