got a 2000 durango with the 5.9. what exhaust tubing diameter do we have. looking to order a muffler to replace the factory one.

 

2.5" A quick search would have answered that easily.

 

The down pipes are 2.25 then go into a Y pipe, from the Y pipe it is 2.5" out through the cat, muffler, and tail pipe.

However on the California Emissions model it should be different, being 2.25 through the CAT's (2 of them) and into the muffler with a 2.5" muffler out to tail pipe.