You're using the wrong terminology to describe the issue.Would not crank but starter would turn. Pulled o2 sensor harness and put in new efi fuse and cranked right up.
The starter motor CRANKS the engine, the same way that a hand crank used to CRANK the engine before there were electric starters.
The engine will FIRE/START/RUN if all systems are working properly.
The EFI circuit and ECU have nothing to do with the starter motor cranking. You can remove them from the truck and the starter motor will still crank the engine. The starter circuit is very simple on these trucks.