Radius

I have a 1991 V1500 Suburban 5.7L 4x4 with 245K mis.heres what's happening. Starts fine, runs fine then simply dies. Also will run and while driving will shut off. When I try to restart I have no dash lights while turning key to on or start and no hazard lights. Headlights work and with key turned to accessory position I have power to the radio. After returning to car one early morning car started fine and I put it into gear and drove off slowly and the key alarm came on and the engine went dead momentarily and came back on.
I continued driving a very short distance and the engine dies again . Now I'm coasting in gear dead in the water for maybe ten seconds and the engine is suddenly running again.
I've changed the starter and solenoid and also the ignition switch .... Can a bad ECM do this ? Or should I look to grounding issues ? Sometimes it cuts out and will allow a restart without further issue . If I change the ECM I'm worried about missing what caused the ECM to go bad in the first place . In addition I ran a check for fault codes and came up with nothing but the 1-2 over and over which I read as signifying the system was working and had nothing stored. Is it time to bury my old friend ?