Sounds like the computer doesn't know how fast the truck is moving, or if its moving.

Run the self test, the KOEO test and see if anything comes up, no light on doesn't mean it won't have a code or two.

Could be the VSS (rear end) or the PSOM (behind the speedo).

Could be a bad connection at the solenoid pack, could be a broken/burnt/pinched wire.

The KOEO test may lead you to the problem, start with that.

Just In case your not sure how to run the test/s here is a link,

Ford Fuel Injection How To Run a Self-Test