Loosing power, 87 s 15 jimmy, after getting warm, tries to die ,can not rev engine, start to backfire, no power,want to die on me, pls. help.

bad need of a tuneup? like new spark plugs, ?
172 , is 02 rich/ lean warning. this one is low oxy for rich.
this code can just be a victim. for sure , with misfire.
means 02 sensor stuck at rich,
what is water temp in engine coolant, at failure? less than 150F?
could be lots of things.
leaking injectors, bad fuel.
injector sticking> causing misfire.
id use a scan tool and watch all sensor when it fails.
too high fuel pressure.
misfires cold, but only luke warm cold starts not fully cold.

just one DTC, no P0300 or 30x misfire codes, not even P0300 pendings?

This almost sounds like the big vacuum line that runs off the back of the throttle body, the one that controls the PCV valve. I would check that first, also clean the PCV valve (should rattle when shaken), it may be stuck open, and look at the vacuum lines that run behind the brake master cylinder, these often get rotten, and are cheap to replace.

A vacuum guage should read between 17 and 22, and, if low may indicate a large vacuum leak. Start there.

Does the fuel line still have 55 PSI when engine warmed up? Any other codes show up?

check for water in oil on dipstick. head gasket? head cracked? need more diagnostics and info.

Try to unplug the mass airflow sensor and start it. It will idle higher but should run fine. If it works then you need a MAF sensor. Be sure you have an OBDII code puller to clear the computer when done

Is the MIL light on on the dash?

Check your intake and exhaust modules. I have a 1987 D21 and had the same problem (if I understand your post). I replaced the modules located behind the driver side headlights and it fixed the problem. Good luck! I hope this helps.

maybe bad ignition module or coil.. when they get hot sometimes they wanna die...

Have you replaced your O2 sensor? If not, try that.