So I have an 06 GT. I’ve changed my plugs,coils and alternator. Now,my alternator has a makeshift power wire on it from AutoZone,if that means anything here. I am going to put the new heavy duty one in today.

But I had bad misfires all over the place. Rough idle. All that. Turns out I had 3 bad plugs. So changed my plugs and coils,and the car ran right juss like when I first got it..... for 5mins. I hit the freeway and all was well,then hit the interstate and the misfires were very noticeable.

I’m not sure what to do next,honestly 🤷🏾 I did buy this used at 167,000,not sure what number owner I am.