My 1999 5.3 L Silverado (66,000 mi.) had a hard time starting when warm(cranking for 3-5 seconds) but would start fine when cold.
I stopped at the dealer yesterday morning on the way to the dump, described the symptoms and he pulled a new fuel pressure regulator off the shelf, and 5-10 minutes later, the truck started fine.
Plus he charged me cost for the part ($47), it's normally ($67).
Thanks to this newsgroup I was able to research and go in with a good idea of what was causing the problem.
Randy