unlocked converter on dyno % loss

[01WS6475hp]

How much will you lose % wise if you dyno with an unlocked stall.Lets say I dynoed 365 rwhp . My dyno guy said my converter was making me read lower numbers.My Max A/F was also 14.62 then it looks like it is 12.07 at the end of the run if I am reading it correct. Do I need a new tune even though my car runs good and strong.Just curious what numbers I should be at.Also have a 12 bolt,3.73 and a midwest 3400 stall.

[speedkills]

I have been told that it is good for .2 to .4 on your e.t. With the 4th gen Fbodys I have been told that the PCM will have to be programed to lock up the converter. My only question is how can this be done with a simple electrical switch?