When my shutoff valve went bad it would shut down instantly, w/o warning, at any speed or driving condition....Was as if key were turned off.
Different than you have clarified yours is reacting.
I think testing the ECU as MBDOC said is your best bet.
If it tests good, I might replace the shutoff valve (if you haven't already) before doing the harness. They are expensive. I know. Mine flew here from Germany (probably first class
).
edit: had the chance to re-read the whole thread again and see you DID replace the shutoff valve.