I need to replace my broken, rusted-out exhaust system. There are far too many to choose from... 
Unless there is a compelling reason to spend the big bucks for a stainless system, I think an aluminized would fit my budget better right now. If I read the old threads correctly, a 4 inch is plenty for my motor. Is that correct? They seem to run about $300 to $350. The Cummins is stock right now but I do want to eventually try to get close to 400hp.
To help on the other end, and to replace the K&N that seems to be in disfavor here, I was considering an S&G air filter with it's enclosed air box. I like the idea of trying to keep the intake air as cool as possible. Looks to be about $200. Any opinions on those?
Are there any particular brands or types of exhaust systems or air filters I should be considering or avoiding besides the K&N that came with my truck?

Unless there is a compelling reason to spend the big bucks for a stainless system, I think an aluminized would fit my budget better right now. If I read the old threads correctly, a 4 inch is plenty for my motor. Is that correct? They seem to run about $300 to $350. The Cummins is stock right now but I do want to eventually try to get close to 400hp.
To help on the other end, and to replace the K&N that seems to be in disfavor here, I was considering an S&G air filter with it's enclosed air box. I like the idea of trying to keep the intake air as cool as possible. Looks to be about $200. Any opinions on those?
Are there any particular brands or types of exhaust systems or air filters I should be considering or avoiding besides the K&N that came with my truck?