01' v6 help plz
 

So I bought my 01' v6 about three months ago, and it has around 211k miles on it. it was pretty babied from what they told me, and didn't start acting up until we came back from Christmas break. It would turn over but not start. We took it to the shop and they fixed that problem, but it seems like its slow on the shift compared to before. it seems to idle at around 550 as well as shakes when idling. My grandfather and I have no idea what its problem is. Plz help.