1987 GMC Suburban MAP Sensor shuts down engine

Remove the TBI unit and check vacuum passages under its gasket as it may be clogged and giving the wrong vacuum reading causing your issues

Yes but we call it TBI
As it an injection system

Let me know

Check timing
loosen distributor and turn a bit
connect all that was disconnected
clean throttle body and idle air control valve
disconnect battery wait and then reconnect
start engine and let it idle
drive it around if possible
if none help
check for codes if any

Are you getting any codes?
Wrong vacuum
bad sensor
timing

This is how the MAP sensor work and when the ECM depend on it
Manifold Absolute Pressure (MAP) Sensor
The MAP sensor is a variable resistor which measures the changes in the intake manifold pressure which result from engine load and speed changes.
The pressure measured by the MAP sensor is the difference between barometric pressure (atmospheric air) and manifold pressure (vacuum).
A closed throttle condition (engine coast down) would produce a low MAP reading while a wide open throttle condition (engine acceleration) would produce a high MAP reading.
The high value is produced because the pressure inside the intake manifold (vacuum) is the same as the pressure outside the manifold (atmospheric air).
The ECM supplies a 5-volt reference signal to the MAP sensor.
As MAP changes, the electrical resistance of the sensor also changes.
By monitoring sensor output voltage, the ECM is informed of intake manifold pressure.
A higher pressure (high voltage) requires more fuel, while a lower pressure (low voltage) requires less fuel.

SO ,When the engine is running above 400 RPM, the ECM operates in the open loop mode.
In open loop, the ECM calculates injector pulse width based upon coolant temperature and manifold absolute pressure.
The engine will remain in open loop operation until the oxygen sensor reaches operating temperature, the coolant temperature reaches a preset temperature, and a specific period of time has elapsed after the engine starts. When all these conditions are met, the ECM operates in the closed loop mode. In closed loop, the ECM controls injector pulse width based upon oxygen sensor signals to maintain the air/fuel mixture ratio

With onlt 17hg of vacuum check for an exhuast restriction, keep the vacuum gauge on the manifold, raise the idle to 2000 RPM, watch gauge, if it starts to fall, the exhaust is restricted. Or it could have weak valve springs, compression check the motor.

Just a note : Catalytic converters is a federal law and not just a state

Yes. Keep us posted I would like to know the outcome, clogged cats will give your symtoms, even a crashed pipe can. BMRFIXIT is right about Fed emmissions, Cats are required by Fed law. Do what you want, but if the state has an inspection sticker program, Fed law supercedes all!

If the cats were badly clogged, take mufflers off and check pipes, these chunks that break off cats can lodge anywhere in the exhaust, if you can remove as much of the system as possible and test drive it. You will find more, especially in muffler.