Huge thanks to all who offered help so far!
Update: We drove the 600km home without any major issues, left at 5am to avoid the heat, and took it easy on the hills. The temperature gauge seemed to work a bit more often than before, and a few times when I noticed a loss of power coming on, it was right at 90C. The gauge typically dies when it reaches around 90C, which could be right when the low speed fan comes on. I have a new switch somewhere, was waiting to install it and now can't find it. They're cheap, I'll get another one.
By keeping speed to 110km/h, I avoided any drama like on the way up - tank was full, and I dumped a bunch of injector cleaner in for good measure. Even small hills on cruise would sometimes cause gradual loss of speed, but adding some pedal would recover; I'm guessing there is a limit of throttle % that cruise will apply, as this has been happening for some time.
The lift pump is dead. Open circuit at the pump connector, and 12V is present across the supply plug when engine is running (and it runs no differently with pump unplugged). 12V for about 1s when key turned on. Now to figure out how to remove the fuel connectors without breaking them, I will search for this procedure.
Does anyone know the specs (pressure/flow rate) for the lift pump? I have one of
these generic fuel pumps as a backup lift pump/fuel polisher for my boat. I wonder if it could service as an emergency pump if the new style lift pump dies? Can fuel circulate through the system when the engine is not running if a pump like this were installed at the filter inlet (for testing/backup)?
I may still have other issues like
vacuum leaks and a
worn cam, but
I will replace known bad parts first, ie: the large cooling fan, coolant sender, and lift pump, and inspect the vac lines and cam when I have time. I have an engine rebuild to get back to (not a VW, a Perkins).
Thanks again.