91 K5 Blazer Code 42 EST Problem

[code420247]

My friends code reader gives A code 42 -Electronic spark timing problem.

I have changed Cap, Rotor, P/U coil and moduals in the distributor, plugs, plugwires and even the throttle body gaskets.

Now ive changed the ECM (the computer)!!! I still get the code 42!!

It all started about A week ago. The truck will die on the road at least once per day but runs OK otherwise. The SES light only comes on when it starts to run rough, which is right before it dies. I'll pull over give it a few mins. and then it starts right up like it never happend.

It all most feels like "Lack of fuel pressure". So I did a pressure test . Just fine At 13 PSI.

Can someone please help? I dont know what else i can do!!