89 B2600 stalling after warm-up

This problem just appeared and progressively has gotten worse. It starts great and runs fine to a point then just completely dies after about five minutes. Doesn't matter if it is at idle or up to speed. After sitting for a few minutes fires right up and may run fine for a indefinite time. At first I thought it was the fuel pump thought I had it licked when I replaced it and ran it all over town without a hitch but No! the problem resumed. when ever it stalls the relay seems to switch on an off several times. Tested the resistivity and it is in spec. I know this is probably a simple problem but it's beyond me so thought I would appeal to those with alot more technical expertise.

I had this same thing happen to me. I ended up replacing the ECM. Actually I had it fixed. I think the company that did it is avpro. I'll try to find it and repost. They're very fast and inexpensive.
I haven't had any trouble like that at all since I replaced mine

I had the exact same prob and sent it to avpro(.com) and they fixed it and retruned it in like a week...now its starting really hard in the cold and died twwice on me today...might be the ecu again or it could be the injectors...i hope its simple, anyways, back to yours...your ecu should be behind the removeable panel by the pasangerside door...you'll need a phillps driver and like 10mm socket to remove the ecu and the plugs are all diferent sizes....open the ecu and look for discoloration around the capacitors...mitsubizy contracted out some bad ones and they leak onto the board. Oh and the more you drive the truck before you get it fixed the more damage to the ecu, so check quick!