Well i believe all of them help and if your trying to really get that feeling then buy all of those parts or get and SRT6.

Yes that is what the sprint booster is for.

How long have you been driving? thats what i want to know. the RPMs fall when it shifts haha that is a good thing. if you stayed in the same gear constantly you would waste huge amounts of gas or blow your engine. your car is trying to save gas by running at a higher gear and a lower RPM.