Was this truck a factory 7.4? When you mentioned flipper made me wonder. I am not the electrical specialist by any means. I think in stickies here the manual can be found or another member sent me a link a long time ago
Are you getting spark? Have to test with a tester. Here a link to my no start thread to try a few things.
Thread '7.4l Now no start' https://www.gmt400.com/threads/7-4l-now-no-start.52786/