Battery Short randomly losing ECM power w/ign on

[Rawze]

sounds to me like you have the dreaded bad ecm (with the well known internal intermittent ribbon cable of hell inside it)... you have replaced the ecm.. it ran for a while,... sounds to me like you got another bad ecm from somewhere... Where was the replacement from? -- if you smack the top of it, and it kills the engine, then simply put, you have most likely yet another bad ecm, simple as that .. I have seen it a hundred times. Only other alternative is that you replace the entire engine wiring harness.

Only other thing I would do is monitor fuel pressure to see if it is not falling off below 250psi while running (or below 75 psi while cranking). If so, could be a snapped shaft on the gear pump that is catching sometimes, and at other times, slipping.