I've had the same slug issue at around 5,000 miles or so. The car drove perfect before then, I've reached speeds of 140+ with no problems and was happy that I could do it even though I would never need to. I drove normal for a few weeks 80-100 mph until a Benz decided to flex his muscle on the parkway. I'm guessing it was a high end E class.

Cruising at 80 mph I decided to give him a run for his money, but instead he blew past me going over 130 like it was nothing. My car wouldn't go past 115 for the life of me. RPMs shot up but now power to the wheels, tranny wouldn't downshift either. The next few days I noticed the car would shift erratically at times (thats why I hate automatics).

I took the car to the dealer, they fixed the car within a few hours. They said some O rings went bad causing a dip in fluid which made the tranny act funny. They replaced the O rings and a plug of some sort. I was so happy thinking I can take on BMWs again. After 40 sec of driving I got the same clunk in shifting. I figured I'd wait a few days to see what happens.

The car shifts fine but at highway speeds I sometimes lose the acceleration, especially coming out of a toll. When I try to hit the 120 mark thats when I get that erratic feeling. Also cruising at 60 mph I get an occasional hiccup in speed. After reading this thread I realized it must be a supercharger issue because the RPMs don't fluctuate during these anomalies. The dealer cant road test with me because the speed limits are only 55 and my problems happen at 80+.

I have the service manual on cd; I'll see what that says before I go to the dealer again with this thread. Hopefully I get my power back, as stated in an earlier post its very dangerous to overtake a vehicle when you don't have the power to do so.