Whilst its possible that its the coil, in my experience, they either work or they don't. If the coil was failing then it would not start well, and misfire at higher revs.
We did a compression test a while back, admittedly before the overheat, but I see no rerason for anything to go bad.. its not like you fried it...

My guess would be something in the FI domain.
You already checked the temp sender, so that was a start.
Do a fuel pressure test, see if something is odd... you know what it was before, see if it changed.
Maybe the EHA went bad?
Leaking cold start injector?
I am also concerned about vac leaks... remember you had that idle hose fail, even tho it was replaced when you got the car.

Another issue is use... are you are doing more short trips with the A/C on full... could be a factor?

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2009 Mercedes ML320 Bluetec