You can add bolt on parts (Catback, Cold Air Intake) along with a Diablo tuner to increase the performance. I did a test on the Diablo tunes with a catback and CAI back in 2013. Not much of anything but a better throttle response. I believe I gained around 10 hp. Not enough to feel driving around. Definitely did not get better gas mileage.
Sounds like gas mileage is important from your post. At 97,000 miles it is time to start looking at what has been changed over the life of the car. You have new plugs and coils from a previous post reporting problems? Has the differential, coolant and transmission fluid been changed in the past 97,000 miles. Also brake fluid, has that been changed. You would be surprised at how much better a car can feel by changing the fluids when it gets to the 100,000 mile mark.
I would say I would like to keep gas mileage where it currently is while also increasing power. If I wanted to only get better gas mileage I would sell this one and get a Prius. But thats no where near as fun. haha!
So I have new coils, plugs, brake fluid, and I am 90% sure the differential fluid was just changed as well. I have never changed the transmission fluid, primarily because the manual only said it was needed at 123,000k miles. I took it to a local and highly rated transmission guy near me, and he said that the transmission on this car shouldn't need its fluids changed till the manual says it should. According to him the stock transmissions on these chargers are top notch. I cant remember of the top of my head when the engine coolant was changed.
I'm thinking next time I bring it in I should just have them replace EVERY fluid in the car, especially since its getting up there in miles.
And correct, about 5 months ago I noticed the car had seriously started to slow down in performance. I wasn't sure what it was, until one day accelerating onto the highway a cylinder 5 misfire code got thrown. I looked up the best way to deal with that and figured out that replacing the ignition coils would be a great place to start. I replaced those and that helped significantly. However a good portion of the performance issues still remained, along with a significant decrease in fuel economy (around 25%). I took it to a mechanic who did a complete diagnostic on it and he said that, according to the cars computer, everything was running perfectly. He did notice the performance issues, so he cleaned the throttle body. That did help quite a bit, but the fuel economy issue remains, and its still not up to 100% power. More like 85%-90%. Still working on that issue. =/
So then with regards to your tuning experience, was it worth it to change it, or is the stock tuning good enough?
Thanks for your response,