When the truck first starts up when cold it won't drive but maybe 5mph but once it drives a couple miles it runs great. What could be the cause?

Diesel engines are cold running monsters. Check the glow plugs:

https://www.askmehelpdesk.com/cars-t...ml#post1415281

I would also recommend that you start using full-synthetic HDDO. When cold, diesels perform much better.