Excessive carbon in the EGR passages seems to be from running rich, which is what happens as the O2's start to go.
Oil blowby gets worse as the miles pile up and is sucked in through the PCV valve. Fresh oil keeps blowby to a minimum. If the PCV valve starts sticking it's even worse.
In a new engine there is only a small amount of reversion of the intake airflow, so little fuel makes it from the cylinder back up through the secondary valve to gunk up the secondary butterfly (remember the injector puts fuel in the primary runner right before the valve).
As the engine ages there is more intake flow reversal durring overlap. This causes increased gunking of the secondaries, and can cause moosing to start somewhere between 50,000 to 80,000 miles.
The exact cause of increased intake flow reverse pulses has not really been explained to my knowledge. If your CAT's are beginning to restrict the exhaust flow that might have something to do with it.
Your apparent IMRC problems are no doubt contributing also.
