I got a 93 flareside with the 5.0 I have converted to 5 speed with transfer. I can't get a starter to work on it. I have tried 3 different starters and they all keep dragging. Work great, once, then it's like the flex plate won't let go of it. What am I missing

 

Are you buying the right starters? Auto and manual trans trucks do use different starters.
When you did this manual swap, did you make sure to reinstall the engine backing plate behind the flywheel?