This will be quite long, I guess, I apologise but I am at my wit's end.

2010 3.6TDV8 SE. 91k miles. It was left in a dry warm garage for about 6 weeks in Feb/March. When I got it out it started normally and quickly went into restricted performance, throwing the following codes (read by iCarSoft LR 3):
P132E-21; U0401-68; U0401-81; U0415-81; U041868; U0159-00.

If I clear the faults with the engine running the engine faults go and it runs fine, but it won't clear the speed sensor codes unless the engine is stopped. If I do that they all come back when I crank it to start.

I assumed low voltage upsetting various ECUs, hence the new battery. No change. Battery 12.5v resting but dips to 6.7v when cranking - according to icarsoft., dips to ~8v on voltmeter.

Then as it seemed the voltage was dropping on cranking, I put a new starter motor on. No change.

Earth problems? Checked them, even ran two new straps from gearbox and bell-housing to body. No change.

Power supply problem? Removed checked and cleaned up the connections to pyro fuse and fusible distribution box behind the battery. No change.
Removed, checked and cleaned fusebox connections and earths. No change.

Borrowed the requisite relays from my wife's 2009 3,6 - no change, and hers ran on my relays. But, here's the strange thing. As a control, I put the icarsoft on hers and found that, like mine, it dips to around 6.7v on cranking - but with no ill effects.

So now a bit stumped where to go next.