89 with 2.8 and auto trans

89 with 2.8 and auto trans. It starts, runs and moves. But stalls every 20 seconds or so. Stalls if driving or just idleing. Stalls then starts right back up. I changed ECM and checked fuel pump. Im stumped. Is there any sensors that would cause this. Only thing I can think of is another ECM change. Maybe I got a bad one at junk yard. Where should I start?

What was the original reason for the ecm change?

I changed the ECM thinking that was the stalling problem. But it still wont stay running with different one. Makes no sense to me.

You checked the fuel pump. Did you change the fuel filter?