I just bought a 2002 SLT3500 dually with an aluminum flatbed. The previous owner damaged the exhaust system. The Dodge dealer I purchased the truck from replaced the muffler and tail pipe. It appears that the pipe going into and coming out of the muffler is 4" but then the tail pipe welded to it is 3". You can see where they butted the two different size pipe together and welded to fill the void. Is this right? Is the stock tailpipe for the 1994-2002 cummins 3" or do I have a problem?

 

My 2002 3500 dulley had a 3" all the way from the exhaust manifold. Replaced all of it with a 4" pipes and muffler.
You could prolly have a 4" put on from the weld.

 

The dealer installed an OEM tail pipe. Cut it off and toss it, and replace it with 4" and you will be much happier.

 

My '96 was 3" turbo down to cat, 4" cat to muffler, 3" tailpipe when I got it. It's now 3" to (gutted) cat, 4" straight back from there, soon to be 4" turbo down, into 5" stacks.