I agree with teknicsrx7 about the cat. The code you ae getting is pretty specific and, generally speaking indicates that the cat in question is no longet functioning properly.
You have replaced the pre/post cat O2s so that eliminates those variables.
As for the 12.7"Hg reading, you need to verify that. Any of the ports on the manifold will do to take a reading. That reading would be bad here at my place (6,500' altitude) where we normally see mid to high 14sHg. Rule of Thumb is that you loose 1"Hg for every 1,000' of altitude due to ambient air pressure drop. Keep in mind that an Inch-Mercury reading is a
relative pressure reading. It represents the pressure differential between the current atmospheric pressure (Bar) and the pressure in the vessel being tested.
Assuming the best case and the manifold pressure is where it should be, the MAP sensor would be suspect. Also MAP really is Manifold
Absolute Pressure. Not Vacuum... The PCM converts the psi
a to a "vacuum" reading for ease of reference as most folks do not deal in absolute air pressures...
Here is a handy dandy test proceedure for you:
(1) Inspect rubber L-shaped fiting from MAP sensor to Throttle Body. Replace as neessary.
(2) Test MAP sensor output voltage at MAP sensor connector between terminals A and B. With ignition ON and engine OFF, output voltage should be 4-to-5 volts. The voltage should drop to 1.5-to-2.1 volts with a
hot neutral idle speed condition.
(3) Test Powertrain Control Module (PCM) cavity A-27 for the same voltage described above to verify wire harness condition. Repair as necessary.
(4) Test MAP sensor supply voltage at sensor connectorbetween terminals A and C with ignition ON. The voltage should be approximately 5 volts (+/-0.5V). Five volts (+/-0.5V) should also be at cavity A-14 of the PCM wire harness connector. Repair or replace wire harness as necessary.
(5) Test the MAP sensor ground circuit at sensor connector terminal A and PCM connector A-4. Repair wire harness if necessary.
And here is the pinout on the MAP sensor:
So, if the voltages are wrong and if the Vacuum gauge reads where it should (In the neighborhood of 20"Hg if you are at an altitude of 1,000' or less) the MAP sensor is shot.
In theory, a perfect engine, at sea level, in a 1 bar atmosphere will develop 21"Hg. It is a rare day that happens. Most days, you will see 17"-20"Hg. Depends on what leaks are present and what the current barometric pressure is and the condition of the engine. If the day is stormy and the barometer is down, so will the vacuum be.
If the volatges are bad and the vacuum reading is bad, you need to start hunting for leaks. Absolute worst case would be that there are engine problems such as intake valves that no longer are seating properly or the rings are well on their way out and the engine can not pull the vacuum.
Hope this helps!