I'd guess it's the resonance flaps. My buddy had a '97 and it had a competetant amount of power but that power really needs the RPMs to deliver. It shifted about 500 RPM higher than the turbo cars.

If the flaps are stuck in the low RPM setting, I'm sure it would feel breathless at higher speeds.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250