Odd... Could it be the engine or trans has moved and now the adjustments are out? Perhapd the coupes are more prone to this due to a different mounting arrangement? I have no idea if they do, just a thought.
My 300CE has 174,100 miles on orginal trans. and its shifts sweeeeet. Ummmm tho overdue a fluid flush.
As Benzmac said, I'd get the adjustments checked, especially the trans. modulator which could be faulty.