Do you plan to do this all at once, or a little at a time like I did? No matter what you decide, I'd recommend you do things in a logical order. You already have the tuner, which is a good starting point. I'd address the exhaust system next. Headers and cat. back systems are a matter of choice, unless you live in a "smog nazi" state. If you're in a smog nazi area, you'll probably be limited to a CARB approved shorty header. If not, you can go with long tubes. On a 5.7 keep the primaries to 1 3/4 in. The larger diameter primaries will work fine, but you'll lose a slight bit of power. For the cat. back, I'd recommend you stick to the stock size tubing, use some sort of straight through mufflers and probably keep the resonators, unless you're going to delete the MDS. Just remember, the resonators are there to help remove any droning.
On my 5.7 Magnum, I run JBA shorty headers, stock tubing with a stock SRT8 "suitcase" muffler and stock SRT8 resonators. With this setup, In MDS mode at less than 2000 RPM, there is what I would describe as a muted bass tone....not really a drone. Above 2000 RPM is quiet but does have a fairly quiet rumble to it, especially at idle.
Next, I'd do the cam.....and lifters if you're going to do the MDS delete. IMO, cam selection is critical, as you do not want to go too radical otherwise you end up with reduced low end power and a terrible idle that you'll have a difficult time tuning it. You currently have VVT, but many of the aftermarket performance cams for the VVT engines are phaser limited or phaser locked and no longer a true VVT engine. This is not a problem. The cams in both of mine are MDS friendly and are one of the keys to the better fuel economy that I get with both of them. I also have both set up with a fixed amount of cam advance to help with the low end power. Maggie is advanced a total of 10 degrees (4 on the cam grind and 6 on the timing), and my Jeep with the same cam is advanced a total of 6 degrees (4 on the cam and 2 on the timing). I also use 6.1 timing chain tensioners on both.
The tuner, exhaust system and cam will probably net you around 75-90 hp....maybe a little more. IMO, you'll also want to do some "tweaking" to the transmission. If you can get yours hands on a "real" Mopar Performance Transmission Control Module, that would be the "cat's meow", and also a Transgo Shift Kit. Otherwise you'll have to use your DS tuner, a CMR tune for the DS unit, or pick up an HP Tuner and spend a few months trying to figure everything out to make it better. My engines and transmissions are both HP tuned, but I started with DS 93 tunes and modified them a bit at a time until I got the best performance and fuel economy. You'll find that, if you go overboard on any of the mods, you'll more than likely not be maximizing your performance or economy and may end up having driveability issues.
Beyond these mods. there are a few more things that will help to lesser degrees.....underdrive crank pulley, catch can, coils, cold air set up (modify the stock one), maybe an 85 mm throttle body, and stuff like that. If you want to get a little more ambitious, you could mill the heads a bit and clean up the ports and port match.....don't do a complete port/polish though unless you're going with forced/nitrous induction or a stroker kit..
