i have the exact problem with my 300D turbo. i have 310K miles on mine automatic and i have the same feeling. you press the gas and hear the engine struggle like it is saying "upshift, upshift" and then when you let off the gas yu feel a gigantic kick, worse when cold. it is like a standard w/out a clutch pedal. It is defintiely the vacuum system and i dont know much about it either. it has something with that blue round component on the right of the engine with all those hoses coming out of it. i would really like to fix that too!