EGR woes

What would cause a 95 Cavalier to hesitate/buck? Happens when you
accelerate into the higher RPM of any gear. Buck, buck, buck. But
then when you shift to the next higher gear it goes away...until you
get to the higher part of that gear. So, it seems to me it's related
to RPM.

I also suspect it has something to do with the EGR system because if I
plug the vacuum going ot the EGR valve the bucking completely
vanishes. Completely. Same thing happens if I disconnect any of the
following: EGR selonoid, MAP sensor, O2 sensor. So it looks like if
I disconnect any piece of the EGR system the problem goes away. With
that in mind, my theory is that some piece of the EGR system is
telling the EGR to open at the wrong time. Is that a fair assessment?

I've changed the following: fuel filter, plugs, wires, crankshaft
position sensor, TPS, MAP sensor, upstream oxygen sensor. EGR
selonolid opens and closes. Vacuum lines looked good, checked all the
grounds.

Has anyone run into this is the past?