I have a 2004.5 5AT and my auto does not downshift when I go WOT in manual mode. I'm not sure if the 2004 5AT does does downshift in WOT since have never driven one.

1) Easiest way to tell if you'rs is an 04 or 04.5, check your VIN:
2004.5 Infiniti G35 = VINs from #800001 and up
2004.5 Infiniti G35 Sedan = VINs from E*4M600001 and up and #F*4M700001 and up

2) The 5AT shift ***** are different between 04 and 04.5 I believe (button on side of stickshift versus front of stick shift:
2004 Shifter


2004.5 Shifter




3) 04.5 should be ULEV-II, while 04s are not (04 is ULEV)

4) ECUs are different, part of the change is to make emissions lower (ULEV vs. ULEV-II)