Honestly I am extremely happy with this car. Best bang for the buck.

Gas wise... all depends on mods of course and what Stage kit your running. Stock its gets a decent amount of mileage. Gas also plays a part on how you drive the car.

Best mods... people will argue on this because some like to stay with the stock pcm and try to prove they will out perform a Stage kit. Personally a WGA is one of the best mods since the stock WGA opens around 4-5psi... you will hit 14.7 psi on the stock wastegate but you will watch it slowly drop with the gas pedal to the ground.

The problem is if you get an aftermarket WGA and you stay with the stock pcm... if your boosting around 17+ (if I remember correctly) you will start throwing overboost codes... some worst then others and you might go into limp mode. Best thing to do to prevent this is purchase a Stage kit first... Stage 1 being the cheapest and IMO a good upgrade. It ignores anything that will hinder performance... overboost codes... downstream O2 sensor... etc.

But you can skip all that and just go Stage 3 with toys and a AGP Stage 3 WGA. Run 320+ hp untuned.

2003 SRT-4's didn't come with the LSD, they had smaller injectors and were rated at 215whp.

2004-2005 SRT-4's came with LSD, Stage 1 injectors and were rated at 230whp.

On my old setup which consisted of 5 performance mods I put down 255whp with 311tq on a DynoJet. This was with the stock turbo, stock O2 housing, stock exhaust manifold, stock intake manifold, stock injectors, stock throttle body. Those numbers were with bolt-ons. Just comes to show what a little bit of mods can do. These are old numbers to me now, I have since switched out some mods and added some more.

I hope this answered any of your questions. If you need help with anything or have anymore questions just ask.