Exhaust Recommendations?

What would be the best exhaust upgrade for an 04`2500 HD 6.0? How about a new computer chip? I have heard so many things to do,but most are a no go.
What would be the best power gains for this truck and would they benefit mileage at all? Mileage is not a huge concern,but I don`t wanna make it worse. P.S.I cant afford a blower!
Thanks in advance, Alex
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