I did some Google-fu on this one and came up empty. Some people have tracked down long cranking times on the Pentastar 3.6 to camshaft sensors but their starting problem was consistent in all temperatures.
Couple things come to mind that no one else mentioned, one is an injector that's leaking. When you start you would have 1 flooded cylinder and 5 starved ones.
The other off the wall thought is winter-summer fuel. Could you be running winter gas that's causing a vapor problem when it gets warm? Possibly a different brand of fuel might make a difference. It's a slim chance on that but doesn't have much cost.
If you have an EVIC on your truck look at the temperatures of the sensors before you start. Look for something that's out of line. A temp sensor could be a bit out of whack.
-Tom