Hey till... it worked!
but I don't know why I had to put the whole prepareDataRow($rec) method inside the list_action class.
Now if you allow me I have more 2 doubts...
On the templates when I put my new 2 variables that is inside the <tmpl_loop name="records">
it's shown, but shows the number of entries on the DB, not a single line... but the SUM value is okay, is there a way to show it outside the "tmpl_loop"?
Secondly, I have an issue related to dates... here in Brazil we use the date format "d/m/Y"... when I add an entry into DB it goes on the "Y-m-d" format. How can I put my date conversion method when I show the entry on the screen?
I could not work yesterday... sorry about the late!