Hello Dave Jones @davejones Just a thought, when I had some issues with my 1987 3.6 cab starting/running years back I tried the usual sensors without much impact I then bought a replacement ECU which cured the problem.
After examining the original I found quite a lot of surface corrosion on the terminals, two sets of multi-connectors from memory, I cleaned up the terminals with alcohol/cleaner and tried refitting original just to see..
Now worked perfectly!
So maybe before you buy a replacement ECU might be worth spending half an hour just removing your existing ECU and giving the contacts and connectors a clean. So many ECU inputs are based on changing resistance of sensors/components than any corrosion can upset the apparent ohms detected.
As you probably know it’s mounted under the passenger foot well carpet on the 3.6 models, an area that can get neglected, even damp. (do disconnect battery first)
As I say just a thought!

Regards, Robin