Car struggling to turn, rumbles, and trouble accelerating?

I have a 98 Ford Mustang with a flashing check engine light, took it to Autozone and was told there's a misfire on 5 (spark plug?) I noticed the car was then having trouble turning on after cranking. Along with that the engine rumbled making the whole car shake and had trouble accelerating. I then installed new spark plugs and spark plug wires. I also installed a new alternator because the old one was going bad. After that the car was running fine. Till just recently its happening again, its struggling turning on, when it does come on the car rumbles a lot and doesn't have much power when accelerating. Any info on what it could be and how to fix it please?

2006 ford mustang v6 4.0 maintenance/improvement?

I have 2006 ford mustang California edition and am looking for advice. What should I do to properly maintain it and keep it in great shape? I would also like to improve it as much as possible so that it can get close to a v8. What should the first few mods be? I know a cold air intake, headers, throttle, but what more is there and what order should I add these in? Any advice would be appreciated thank you

Which is exhaust would be the best?

I have a 2003 Ford Mustang V6 with a stock exhaust system. I'm looking to change it to a dual exhaust. I saw that I can get a dual exhaust converter that hooks up to the factory Y pipe for $350 on American Muscle buy would it be better to spend more and change the pipes to either H or X pipes instead of hooking up the converter? I'm cheap so that's why I'm asking lol

Can I transfer my car payments and car to a 17year old from a buy here pay here place?

I have a good question… I got a 98 jeep grand Cherokee limited from ridenowautosales.com I'm still currently making payments. A family friend told me he d sell me his 98 Ford v8 supercharged mustang for 500$ because he needs it gone. Back to the question, my friend is 17 and desperately needs a car would I be able to transfer the jeep and payments into his name? I love the jeep and all but not the 10mpg any help would be awesome!