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JimT

First, what's the odometer reading? Second, are you getting any white/grey smoke while driving during an active regen? Smell of unburnt fuel?

What's your oil consumption like?

If you've done a complete EGR tuneup as Rawze mentioned and detailed in many other posts on this site (and in some videos found above) and there are no exhaust leaks and the DPF injector is functioning properly and not clogged up with soot, then I'd start to focus on some combination of excessive oil (or coolant) in the exhaust stream and/or a clogged/failing DOC. There's also a stuck EGR valve that could contribute to this problem.

Parked/Forced regen works because of the controlled setting. Engine speed is constant, all variables and outside factors remain mostly static. Active regens however need to adapt to constantly changing conditions and any one item out of spec could screw up the entire system.

Also, as the engine ages and consumes more oil that affects DPF soot and ash loads. At the same time as the DOC ages it's effectiveness diminishes. It seems on these 2250/2350 engines that somewhere in the 450,000 mile to 600,000 mile range, depending on how they were maintained and operated, the declining health of both converge to create a situation similar to what you described. Parked/Forced regens work while Active and Passive regen fail. Regens in general become more frequent and less effective. Eventually the system just can't cope and you get plugged up DPF's leading to derates, stop engine lights, possible tows and $15,000 worth of replacement exhaust components. --- Not saying you're here right now, just generalizing the downward spiral I've seen described time and again.