Can the ECM be tested to see if it is bad or failing

How can I test my ECM I think its bad 1991 chevy suburban R1500 5.7 L TBI I have changed the entire fuel system and it still keep dieing.I have spent so much money replacing part after part I cant burn it now. New ICM, distribter cap, rotor, fuel pump, filter, air cleaner, ECT sensor thermastat 160*, knock sensor, oil pressure switch, engine temp sensor on the left head, plugs, wires, TBI kit no vaccum leaks it started acting like it would lose power to the fuel pump die and in a while start up and run great then die like the fuel was shut off or you turned the key off just driving down the road this has been going on for about 7or8 mounths replace a few parts and it runs a day or two and starts dieing again 8mo. Ago I replaced the knock sensor becase I had that code: and when the transmission would downshift for passing the check engine lite would come on thats the only code: that flashed then a mounth or so it starts acting like it running out if fuel I replace filter and pump runs 2or3 days and dose it again pull the tank and the rubber line on top of the pump is busted replaced that runs a day so I put a TBI kit in the fuel pressure reg. Was caked full of varnish grease. It ran for about 2 mounths now its back just this time the code was engine coolant temp my gauge has been setting above 260* before I got it I replaced the sensors and the gauge is still setting in the same place I had noticed my oil pressure gauge going up to 60lbs and down to 30lbs but after replacing oil press. Sw it was steddy about 30lbs found some bad wires repaired or replaced those it will only run about 5 min. And turns off like you turned the key off. No knocking the thing sounds good it just dies as much trouble as it giving me I know it is a good engine just what is giving me so much hell