I have to hold key in start position for truck to stay running?

It sounds like the switch is out of adjustment.

You have a problem with the wiring at the ignition switch,the red/green wire must be broken, or the ignition module needs to be replaced, here is the ignition switch wiring diagrams so you can see what I am talking about and the location of the ignition module so you can swap it out. This guide can help test the wiring.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Check out the images (below). Let us know how it goes