Struggling with a hiccup...

93 3.0 The issue is at idle you can very faintly hear a hiccup every so often but you really have to listen as it is pretty smooth - if you throttle up to say 1700rpm - it will run for a bit then drop 200-300 rpm then jump back up - over and over. --------..--------..--------..--------..---- that sort of thing. If you hold the throttle higher (3000rpm) it just runs rough.

To date the following are all new: fuel pump, fuel pressure regulator, O2 sensor (Bosch), all vacuum lines, plugs, wires, cap, rotor, distributor, ignition coil, igniter, intake gasket, PCV valve, had the ECU all tested OK.

Any ideas? Please... lossing my mind over this...