What's the Next Step

Just replaced the stock muffler on my '05 with a flowmaster super 44, what should I do next to increase hp and bring out all the sound of flowmaster?

That's also the only performance mod I've done so far

If you're going to keep the stock exhaust manifolds I would suggest replacing the restrictive factory y-pipe. If you're planning on replacing the stock manifolds with headers then I would wait to address the y-pipe. Aside from that you could do an air intake, tuner, electric fan, gears, converter, shift kit/valve body, crank pulley, cam. Lots of options. Depends on what you want and do with the truck I'd say. Some of those things I wouldn't do before others. For example i would not install a larger cam in an otherwise stock truck. And there are supporting mods that can be a good idea no matter what you do with the truck like a larger trans cooler and/or deeper trans pan. I'd say generally you want to start out with easy stuff like bolt-ons, then the more in depth stuff like the gears, tuner, converter, cam, etc.

I'm assuming this is a Hemi truck in that reply as well.

/\ This, SublimeRT summed it up pretty well.

If I replaced the y pipe would I need to replace the pipe between there and the muffler? It's all factory piping

The Y should match up to your factory mid pipe.

Personally I wouldn't change a Y pipe unless I was changing the stock manifolds out too. Otherwise you'll be swapping one 2.5" Y pipe for another.. with new headers you can up that to a 3" Y pipe.

Best bang for the buck "simple" mods are a good CAI and a tuner... thats pretty much where everyone starts. And if it's noise your after you can't beat the sound a CAI will give you. They make HEMI's really grunt, in the cabin at least.

It's not just swapping one 2.5" pipe for another. It's swapping 2 pipes smashed halfway to fit into another pipe for 2 pipes properly merged into one that is much less restrictive. If making more power is what you want, it needs to go at some point. Like I said though, if headers are in the plan eventually then you might as well wait to address the y-pipe so you don't potentially have to redo it again to fit the headers.

Here's a pic I found of the merge in the stock y-pipe.




What it looks like on the outside.



Replacing the factory y doesn't have to be the next step, but once again if making more power is the goal then it needs to go at some point.

Even with replacing the factory y pipe and your muffler you most likely wont increase in HP much (say maybe 5 HP). Even adding a CAI isn't going to really add ponies to the truck. You will probably feel better throttle response doing all of them but to add HP you will want a tuner to go along with the exhaust and CAI. After that you can start going into more serious power adders such as long tube headers and cams and custom tunes.

Also, I know you probably don't want to hear this but for the best HP you need the best flow for your exhaust. Flowmaster, though loud, is not the best flowing exhaust. They are chambered mufflers. If you want the absolute most out of everything, you'll want a straight though design like Magnaflow. This will give you the best flwo of exhaust and allow you to access as much HP as possible.