I just got my 99 GTP back from the shop where they were installing a new s/c gasket and TB gasket. I took it out for a drive and it seems to me like the motors working harder then it needs to be with higher rpms. Like I stop at a set of light and before it would idle at about 800RPM now it's at 1100/1200RPM and when I put it in neutral it sits at around 1700+RPM. Due to the higher RPM Its using more fuel. Also at idle my Vac gauge sits around 10 when I swore before it was around 20. I'm no mechanic but I can work on a car and try changing things so if theres any a advice on what this issue could be and what I could try doing to fix it would greatly appreciate it.