You said, "Unfortunately, now that I have all that power back, I'm noticing a very hard shift into overdrive. Every time it shifts into high gear there is a nasty thud, unless your foot is FIRMLY in the throttle, then the shift is fine."

Having your foot firmly in the throttle would cause a harder shift, not a softer shift. A thud unless your foot is firmly in the throttle implies play in the driveline.

Which way do you intend to turn the modulator adjuster? I would assume you want to soften the shifts. It would be unusual to have the shifts get harder as the trans wears. Normally the modulator would need to be adjusted to shift a bit harder, unless someone has tampered with the adjustment aleady and brought the pressures up too high.

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2012 E350
2006 Callaway SC560

Perhaps I overstated by emphasising the word firmly. If I accelerate, even mildly, all the way through the shift points, the shifts tend to occur at higher rpm and are fine - crisp but smooth and no thunk. If I start to accelerate and then have to back off the throttle for another vehicle, and the car shifts during that low throttle period, the shift is hard and sometimes shifts twice fairly quickly and into high gear. Also, If I take off like an old lady, with my foot barely on the accelerator, the shifts occur at lower rpms and are hard and it thunks.

So, what I am concluding, is that when the shifting is occuring under conditions where the vacuume would be very low, it shifts ok. If it is shifting under conditions where the vacuume would be high, it shifts too hard and thunks. This makes me think the modulator is set too high. Maybe the PO or his mechanic screwed with it, I don't know.

The flex disks appear to be fine, and the rear does not appear to have excessive backlash. The trans was just serviced. This was not happening when the car was running under somewhat lower power output before I had the head refurbished.

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Andy_M
'98 W140 S320 Black/Black
'06 W164 ML500 AMG White/Grey
'03 Porsche 986 Midnight Blue/Grey

I wonder if you ended up with a vacuum leak during the head R&R. You might check that vacuum line where it goes down from the top of the intake manifold.

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2012 E350
2006 Callaway SC560

Will do.

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Andy_M
'98 W140 S320 Black/Black
'06 W164 ML500 AMG White/Grey
'03 Porsche 986 Midnight Blue/Grey