My stock 03 muffler was terrible. It was so choked, it hissed like I had a smashed tailpipe, when towing. You already have 4" and that is enough. A 4" straight thru muffler is all I would do to your exh. The air intake stuff isn't worth the money. Do a search on the home depot CAI mod. Guys cut a hole in the bottom of the air filter box and use HD cheap parts to get more cold air from down lower. It's also good to get more air in the bottom of the box when you put in the newer deeper filters. Gauges (at least a pyro) are nice but not necessary til you add fuel. It's scary how hot some of the stock diesels run and you will be helping the egt a little with 2 cheap mods... muffler and the hd cai. I put a pre-turbo pyro in a fiends CTD and it was going over 1400. He took it to Cummins to see why it ran such high egt and they moved the probe to after the turbo and told him... there it's fixed, quit worrying about it! Craig
