The transmission is vastly better with a good tune. (TCM Tune)
You will need to check with your tuner though as to if it comes with or without an engine tune (PCM Tune).
(Some will charge extra as it is an extra separate tune file, and some may throw it in for free, depending on whom and how much they charge for the PCM tune).
I have mine tuned so as with light throttle, gear changes are very early, (To conserve fuel), and I have opted for firmer transmission shifts.
This has almost removed the harsh very low speed 2nd->1st gear change with throttle application shift. (Its still there, but I can always play with it later to try and make things better).
In Sport mode, my thing holds gears for much longer than the standard Auto Tune, and is much more willing to kick down on light throttle applications.
Also one thing to look out for, if you want an L98, then you will be looking at an early CalaisV. (I think MY07 to MY09).
This means the Series II models will be out (So no Holden IQ and Sat Nav will be an option), but also means that you should get some of the goodies that were pulled on later models (Like the 8 way passenger power seat, and RSE/DVD Player that was pulled on the Series II models).
I hope this helps.