Tune help needed

[KDub9]

Sorry this is probably a big-time Noob question. I need some help on what steps I should take to properly tune my cm871. I purchased a truck that was already mandated. Probably not the best decision but it was just freshly overhauled. Oil ran clean for about the first 3000 miles then went Pitch Black.
From what I gathered there is some software that I need to download in order to extract files from my ECM and also a piece of Hardware that I will probably need to plug in with.
Any details would be greatly appreciated.
I'm getting about four and a half miles per gallon and I've been pretty easy on her too. I know there could be many other underlying issues but I feel like a tune is a step in the right direction.
On behalf of my wife my boys and myself I want to thank you for any advice on this subject , it truly can have a deep impact on all of our lives. Thank you in advance.