V8 T5 box is much more rare/expensive than a 6cyl one though..
i did see a transit van once with a commodore V8 T5 adapted .. wondered if this was the reason also.. or if it was a commo V6 one.. shifter location is spot on for the XF to EL 6cyl T5, is another to consider. and cross member issues potential etc
Possibly could have some dirt or something spilled down into the shifter, which relies on switches triggered by the shift lever to tell the computer when to shift up or down. I saw lots of crap build up in there when we had BA-BF Falcons.