hi ,have you checked fuel supply pressure. possible squashed bent hose or pipe if fuel supply good do a visual check of all connectors and grounds if OK.
check power supply to ECM.using an LED test light check battery power to pin #48,52,and 53(red) of the ECM. use ECM pin #61,63 and 65 (black) as the return for the test light
if this is ok and the test light stays lit, check the key switch input to the ECM pin #70 (Orange) if the test light cycles between on and off check that no after market shut device is activating and causing the problem. also check your ground level shut down circuit has not been engaged
I Have come across a similar problem like this before. it appears you have access to ET. go into the status groups and monitor engine parameters, watch closely and obserb any cyclic changes across the parameters. if they are there they tend to average about 8 seconds between cycles this is too short a time frame for the ECM to log faults and usually means something is overloading the ECM internal circuit protection.this can be either internal or external to The ECM.
the easiest way is to use a test ECM and temporarily connect to engine and try. or you can isolate circuits one by one at the ECM and try and isolate by elimination
if you find that the ECM is faulty use the ET function to copy the config files which will record most of your settings including injector trim files. however you will still need to do a timing calibration once you fit the new Ecm
usually if the ECM is that far gone the copy config file part of ET wont work .if that is the case you need to manually do a product status report if possible and re enter the settings by hand. you may have to remove the rocker covers and record the injector serial numbers and obtain trim files from sis in really bad cases