If you can't fire the starter from the ignition switch AND the shift interlock is not releasing, it sounds like you're not getting power to/from the ignition switch.
This should be pretty easy to verify with a multimeter.
If you turn the key to RUN/ON, do the gauges come alive and do the wipers work?
With the key in the ON/RUN position, do you have +12 at the 7.5amp IGN fuse by the driver's left knee?
You said in a previous post that you replaced the fusible link. There are 3 fusible links that come as a single bonded ring terminal that attaches to the positive battery terminal. The 3 links off of that feed different sub-circuits of the truck. Was yours an OEM part?
This should be pretty easy to verify with a multimeter.
If you turn the key to RUN/ON, do the gauges come alive and do the wipers work?
With the key in the ON/RUN position, do you have +12 at the 7.5amp IGN fuse by the driver's left knee?
You said in a previous post that you replaced the fusible link. There are 3 fusible links that come as a single bonded ring terminal that attaches to the positive battery terminal. The 3 links off of that feed different sub-circuits of the truck. Was yours an OEM part?