Wits end 1992 Dodge D150

[tsubaki]

5.2L, MPFI & automatic transmission.
I've been beating my head on this vehicle on and off for 5 years. After letting it sit for the last 2 years I figured I'd attempt to find the problem AGAIN.
In the past the truck would crank up and run flawlessly but at some point it will shut off and not restart, having to be wreckered in. It might sit up and then by some miracle start running fine or even replacing a part might make it run fine only to be wreckered back in.
NOW, it will crank up and run for several seconds, then shut off and not restart. After that if the key is left in the on position the coil stays energized and the injectors appear to be spraying fuel into the cylinders.
The reason I say this is I removed the coil wire and attached another coil wire with a spark plug on the other end, it would jump a continuous arc for 2 inches to anything it can ground to. I also drained the crankcase of 9 quarts of fuel.
This has been going on all along but I couldn't get the vehicle to reproduce the problem to where I could catch it.
Any Ideas??
Timing and chain appear to be good, compression stroke at TDC on mark. Fuel has been drained and replaced.
This is a list of replaced parts (somewhat it order) from the last 5 years with probably less than 500 miles of operation trying to find this problem. Other minor things also have been replaced.
Distributor ignition pickup
Crankshaft position sensor
Powertrain control module
Fuel pump
Auto shutdown relay / fuel pump relay
Ignition switch
Idle air control valve
MAP sensor
Coil
Oxygen sensor
Throttle position sensor
Fuel pressure regulator
I've got over $850 just in parts, some replaced twice.
I'm way past arbitrarily replacing parts, just give me some ideas.
In reference to the above mentioned continuous arc/injector spraying situation, if I unplug the 2 wire connector to the coil and stick a test light from the battery positive to one of the wire terminals I get a very rapid pulse. This indicates to me something is signaling the injectors and coil to operate at a high frequency much like full throttle situation.

Any ideas?