I used to get frustrated about the acceleration issue on my '91 420. I thought it was just a smaller engine issue because I've driven the 5.6 liter and it gave more of a kick off the line.
After I had the transmission serviced (fluid/filter change), I discovered that kick down had not really be working. It works now and while I don't get pinned to my seat, acceleration's better than it was.
1991 560SEL (254K miles)
1980 Lincoln Mark VI - Givenchy
1979 Lincoln Mark V Collector's Series
1979 Lincoln Town Car Collector's Series
1979 Ford "Effie" Pickup (in gradual transformation to a show/street truck)
1969 Lincoln Mark III (waiting for "Overhaulin" to call)
1989 Lincoln Towncar
2001 Lexus GS300 (spousal unit's daily driver)