Have a 1987 Chrysler New Yorker, starts the engine hesitating and will shut off

Sure would be nice to know the engine size when we're discussing an engine running problem. The 2.2L only runs about 15 pounds of fuel pressure. That won't squirt very far. The 3.0L should have around 45 pounds.

Chrysler pumps usually fail to start up when they have high mileage, but pressure once they're running isn't a common problem. What CAN happen is the pickup screen in the tank collapses or gets plugged. That normally shows up when the largest volume of gas is being pumped, which is during coasting. The engine will run better at higher speeds and when accelerating. The only way to know for sure is with a fuel pressure gauge.

Code 12 means the battery was disconnected within the last 50 starts. Code 55 just means "end of message". You'll get that one every time. There are no direct codes relating to the fuel supply system so it looks like you're looking in the right area, but be aware a failing MAP sensor can cause problems similar to what you described. As long as its signal voltage remains between 0.5 and 4.5 volts, no fault code will be set, but if it reports the wrong value within that range, the engine can run very poorly. One potential clue to that is the engine will continue to run, (poorly) as long as the gas pedal is moving. It will stall at any speed if you hold the gas pedal steady.

Check the vacuum hose to that sensor too. There should be two hoses running side by side, connected with a pair of tee fittings, one on each end. That was a recall to prevent fuel vapor from condensing in the hose and deteriorating the protective gel in the sensor.

Sure sounds like a bad MAP sensor.