Mindful of the caveats about running the ZF for extended periods in neutral, while doing gas system tuning I put the T-box in neutral and the main box in D.
after some faffing, which of course gets the engine rather hot, with limited airflow (and yes, on this one, the viscous fan does cut back in!) I took it up the road.
subsequently had iffy gear selection from neutral and temporary loss of drive in any direction. Stopping the engine for a few seconds restored drive.
Low oil, or overheating, or both?
interestingly, the instructions in the HBOL for oil level checking are, IIRC, wrong: says to check at normal operating temp, whereas I thought the ZF was checked when cold, at idle, after running through all the selector positions down to 1 and back up to N.
AFAIK the box is good - it worked OK when I had it before, anyway.