I had a similar problem on my 560 SEL and replaced the coil and wires from advise in this forum and has been perfect since. Did you change the lead from the coil to the cap when you did the wires? When I did my wires I found that wire was difficult to get at and the previous owner had not chnaged it. It was stiff and I suspect it may have been the root cause of my troubles. Definitely an ignition problem IMHO.

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Nokandolah
88 560 SEL 285,000 miles
82 300SD 126,000
94 Ford Explorer 186,00
07 Hyundai Azera 10,000