Need Advice

I have 50K on my Duramax and am ready to turn it up a little. I bought the truck new and the only one who has ever driven it. It is strong, and occasionally I pull my 13000 pound 35 CKQ Camper down to Bristol, or Georgia, and sometimes over to Michigan.

I'm thinking MBRP 5" CATBACK with a 6" Tip. I'm thinking that'll give me the three things I'm looking for: deeper sound, a little more HP, and perhaps a little better mileage. Will that do it?

Should I change the air intake system or go stock? From what I read here stock is OK with a good clean filter.

Thanks for your suggestions.