I am looking for suggestion for and exhaust upgrade for towing. Ihave an 07 Supercrew 5.4l and I frequently tow a 24' travel trailer. I would like to see if I can pick up some more power and torque with tuner and exhaust. As far as the exhaust goes, I want the power without the sound. Would I be best to leave it the way it is, replace the stock muffler, or get a whole new system?

 

I was looking for exactly the same as you are, more torque / power but quiet exhaust. I purchased a Magnaflow 16612 catback kit and it had noticable sound but tolerable even when towing. I ran with it for over a year. A few weeks ago, I pulled it off and put the stock exhaust back on and noticed a big improvement in low end torque especially towing. The OE exhaust is better for low end power but passing power was better with the performance exhaust.
This is what I noticed and because I tow quite frequently, I am now sticking with the OE exhaust. For everyday driving the truck performed better with the Magnaflow exhaust though...

 

I would suggest a 18" or 22" magnflow oval muffler, it will give you the torque and keep the noise levels low.

 

I would do a si/do 18" body Magnaflow with side exit 3.5x18 tips.

 

You can just replace the muffler and leave it exiting in the stock location, but that's boring.

I'd go with one of the bigger Magnaflows to keep it quiet and exit the tips either in front of the rear tire or behind both tires. That will keep the exhaust from dirtying the front of your TT and keep the sound level down since it won't be bouncing off the front of your TT.

Plus you can have some nice chrome tips.

 

I use a single 3"gibson and the sound with the stock intake was no different in the cab than the stock exhaust ( NICE sound outside not loud) and no low end torque loss. I tow a 22 ft trailer into the mountains alot and need all the torque I can get . I have a cai and wish I had left my intake stock with an "aftermarket of your choice " drop in filter. The cai gives me much more go at freeway speeds but I have lost some torque and the noise under load is not pleasant at all to me., now I am going to buy a tuner to get back the torque and fix the drone under load. I hope or it is off with the intake. Some people like the noise of the intake but if you are going to be in the truck for a few hours with a load it does get tireing..

 

I found the Magnaflow was too loud for me in the cab when towing and there was a noticeable loss of low end torque. Sounds like I may have to try the Gibson. The stock exhaust is nice and quiet when towing but it's a little too quiet...

 

Honestly, I would keep it stock if I were you.

Most exhaust setups move the powerband up...which is not what you want for towing...you want it down low, like the stock exhaust has it. And since your not really wanting the extra sound.....