I also have a 94 with no EGR. I bought this truck new, have had it for almost 20 yrs now. I just replaced the engine, and am having a similar problem, but now that I think about it, it may have been doing it before I replaced the engine. I replaced the engine because it had 287,000 miles on it, not because of this problem. I drove it for a few months with the MAF sensor unplugged.
The truck doesn't want to start when cold. It starts right up, and dies. After 4 or 5 attempts, it will run. After driving it a few miles, when it reaches operating temperature, it will quit again. I unplugged the MAF sensor, and it will run, but rough.
I have performed the jumper wire test on the EEC plug shown in my repair manual. I am getting 2 different codes. One is 157, which my book says is low voltage to the MAF sensor. I have replaced the sensor 3 times, same problem. The other code is 998. My book says "hard fault present". I'm not sure, but believe it may be the ECU going out. I thought maybe it could be the PCM, but my local Ford dealer says that the PCM rarely ever goes out??? This may also be the source of my 157 code as well.
I am going to pull the ECU and take it to my local carquest auto parts. They said they will have it tested for free.......sounds good to me, as I don't know what "hard fault present" means, and my book doesn't tell me.
I don't know if we have the same problem, as you said you have replaced your ECU, but I will let you when I find my problem. I don't know if this helps, but I have bought bad "new" parts more than once. Maybe someone out there can shed some light on this subject.
Any help would be appreciated......scratching my as well, but determined to find the problem