Is there a way to test a muffler? Sounds odd I know but I'd like to know that it's fine before continuing with any mods. I know some people run straight pipes but I'd like to keep it hushed as possible.

 

You can always go aftermarket with something that breathes a little better and keep things quiet, but from what I am told the stock mufflers were never a problem spot.
Without a whole mess of sophisticated ways to measure pressures I don't know of a way to test a muffler, short of cutting it apart if you suspect a blockage.
I would be more concerned about the cats.

 

When using a muffler, Magna Flow always showed that they didn't restrict flow and carried a live time warranty.
If I has to choose one, that would be my choice.

 

I ditched the cat, which when removed looked visually very clear, however the kid I bought the truck from said that when they removed the cat the truck ran a whole bunch better so he was a bit suspect that the muffler had a restriction. Now, the engine was in poor health so maybe that was more the issue but I'm just trying to eliminate the easy stuff going forward. It says ford on it so I'm assuming it's a stock muf.

 

I run a straight pipe as do most, look elsewhere, it's a motor issue most likely causing you issue, not a muffler.

 

So aside from lower egt why run a straight pipe? This truck is fairly noisy even muffled and noise isn't my joy in life.

 

If your looking for performance from muffler, there all about the same.

 

True, but most of the sound is coming from under the hood. A straight piped 6.0L is really not significantly louder. I run straight piped too. I do have the stock cat on her due to emissions testing, but its hollow.