1989 D21 PU runs good, but a month or so ago on the freeway it felt like it shut off for a split second. The past few days it suddenly became more frequent so I replaced the plugs, plug wires, distributor cap & rotor, pulled the seat and did each diagnostic mode in the ECU and the only thing that came up was 32 (EGR valve) but did the finger test and the valve seems to be functioning. I also tested the coils which were fine. But it still does it and it feels like it just shuts off for .1 seconds. I used a stick to move some of the wiring around while it was running in the driveway but could not reproduce the problem. I am stuck and need input.