1990 c1500/v-8 at times hesitates pulling off. It sometimes wont take the required fuel to throttle body unless its accelerated hard and then sometimes it will still hesitate like the engines cutting out. Sometimes while driving, "service engine" indicator will appear and the problem will start again. At times, it runs great. Ive changed all sensors, egr, even added a new distributor, wires and plugs. No change.( What do I need to do? )

Hi annie_bryant, I want to help you with your question, but I need more information from you. Can you please add details in the comment box? Did you also change the MAP sensor? Here is a procedure for testing it.

Backprobe with a high impedance voltmeter at MAP sensor terminals A and C.
With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.
If the voltage is not as specified, either the wiring to the MAP sensor or the ECM may be faulty. Correct any wiring or ECM faults before continuing test.
Backprobe with the high impotence voltmeter at MAP sensor terminals B and A.
Verify that the sensor voltage is approximately 0.5 volts with the engine not running (at sea level).
Record MAP sensor voltage with the key ON and engine off.
Start the vehicle.
Verify that the sensor voltage is greater than 1.5 volts (above the recorded reading) at idle.
Verify that the sensor voltage increases to approximately 4.5. volts (above the recorded reading) at Wide Open Throttle (WOT).
If the sensor voltage is as specified, the sensor is functioning properly.
If the sensor voltage is not as specified, check the sensor and the sensor vacuum source for a leak or a restriction. If no leaks or restrictions are found, the sensor may be defective and should be replaced. Hi annie_bryant, I want to help you with your question, but I need more information from you. Can you please add details in the comment box? Did you also change the MAP sensor? Here is a procedure for testing it. Backprobe with a high impedance voltmeter at MAP sensor terminals A and C. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts. If the voltage is not as specified, either the wiring to the MAP sensor or the ECM may be faulty. Correct any wiring or ECM faults before continuing test. Backprobe with the high impotence voltmeter at MAP sensor terminals B and A. Verify that the sensor voltage is approximately 0.5 volts with the engine not running (at sea level). Record MAP sensor voltage with the key ON and engine off. Start the vehicle. Verify that the sensor voltage is greater than 1.5 volts (above the recorded reading) at idle. Verify that the sensor voltage increases to approximately 4.5. volts (above the recorded reading) at Wide Open Throttle (WOT). If the sensor voltage is as specified, the sensor is functioning properly. If the sensor voltage is not as specified, check the sensor and the sensor vacuum source for a leak or a restriction. If no leaks or restrictions are found, the sensor may be defective and should be replaced.