New to tuning

What have is my motor has already been flashed and I have drove it several times , but it seems to be lacking power . I had some one else do the flash and don't have hp tuners at the moment , I was wondering what would the process for me to get my own hp tuners programmer and doing this myself?
2004 6.0
4l80r trans
Ls1 intake
Rear O2 sensor removed
Nothing fancy just wanting it to run better . Thank you

the process is buy HP tuners pro and read read read. It has taken me about 4 or so months but I just tuned my Camaro after installing a supercharger and it run really well..or buy hp tuners and pay someone to remote tune it..