Trouble starting when engine is partially warm

geiselbob

I have a 2003 Silverado 5.3 V8. When I start the truck fully cold or fully hot it starts without an issue right away. When the engine is partially warm it will crank for a while before it starts. What would cause this? It just started over the past couple of months. I've replaced the starter for other issues a year ago and the fuel pump was replaced about two years ago.