I've been having a problem with my 2000 GTP for a few weeks now. When I start it up it has a rough idle and every few days or so it will die while its in idle. Also when I have it in WOT the boost gauge only goes about half way up at the most and there is a noticeable decrease in power as well as a slight "whistle" noise coming from the engine. I'm also noticing a drog in my mpg. I'm thinking it might be a vacuum leak but I have no clue as how to check for one or go about fixing it, any suggestions would help.