Well I can't speak for a '92 truck, but on my own '89 Silverado 5.0L engine, unplugging my MAP only made matters worse. Much worse. Wouldn't idle at all, didn't have any power.
Print this out and have your mechanic test your MAP, or do this yourself. It is VERY important to use a good multimeter/volt meter for this, or risk trashing ECM - DO NOT USE A TEST LIGHT.
Backprobe with a high impedance voltmeter at MAP sensor terminals A and C.
With the key ON and engine off, the voltmeter reading should beapproximately 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 a high impedance voltmeter at MAP sensor terminals B and A.
Verify that the sensor voltage is approximately 0.5 volts with the engine not running.
Start the vehicle.
Verify that the sensor voltage is greater than 1.5 volts at idle.
Verify that the sensor voltage increases to approximately 4.5. volts 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.
I'm still worried about that code for the MAP. Do you remember/know what number the code was? Definitely replace the FPR though. I'm not saying anybody else's suggestions are wrong, but your MAP code could likely be causing issues - like the sensor telling the computer that you're at WOT - which would in turn make your fuel trim go super rich to keep the engine alive at high RPM.
Just thoughts. Doesn't make 'em correct, but testing the MAP is easy as long as you're: A) Careful, B) using good equipment. You can always print that off and have your mechanic do it.
PS: I used my snap-on multimeter for this job this week. I was scared of roasting my ECU. DO NOT SHORT THE PINS.