Sounds like the orifice might be too big, or the foul air pickup is in a bad location.
When you go to a fixed orifice PCV "valve" you are introducing a calibrated leak that is designed to pull air through the engine.
Unless the air goes sonic through the valve, you are operating on the principle of higer pressure ratio across the valve (baisically atmospheric pressure versus intake manifold pressure) makes higher flow. This means that in general, the higher the difference between the two, the more flow you get through the system. If you get a time when the engine is going fast (slinging oil, making mist, etc) AND the manifold pressure is low, you have a 4.2 liter oil suction device.
Sounds like that is the problem cited in the TSB. These can be maneuvers like going down an hill in a lower gear where the car is pushing the engine.
An actual "valve" was designed to restrict the flow at high ratios and not to restrict it a low ratios, these were introduced at a time when carb-a-tooters were the only technology we had and they could not tolerate an orifice PCV system. A "perfect" PCV valve would give you the same flow, regardless of pressure ratio. These have a few moving parts inside them, and have manufacturing variablity that affects flow more than you might think, so they are going the way of ox yokes and dodo birds.
An orifice PCV system has no moving parts, and the only tolerance that has an effect on the flow is the hole size, which is pretty easy to control. This means they tend to be more reliable, simpler, and do not drift over time the way a valve based design does.
However, putting a smaller orifice means that all of the time you are NOT pulling over oil, you are getting less overall flow. If the engine is a borderline sludge-monster to begin with, this could make a bad problem worse. If it were mine, I'd see what I could do about adding an external catch-can.
I'm not that familiar with the PCV system on that engine, and some of the GM ones are literally part of the intake manifold, which makes changes pretty tough. The TSB probably includes a different baffle system that separates the oil from the foul air better.