It seems to be a very steep learning curve for many.
I looked at these things as I started out.

I bought my Power Vision a little over two years ago.

 

Here is another overview of the HD EFI system and tuning:

http://www530.pair.com/rowand/efibas...I%20Basics.pdf

A more basic EFI overview:

http://www.megamanual.com/begintuning.htm