My 1997 5.7 Vortec with 145k has always fired right up after less than a second of cranking. Now it will sometimes take up to three seconds of cranking before it starts. However, it only happens when the truck has been off for 1-6 hours. Fires right up in the morning or when I had just had it running. But when I go to start it when I go to lunch (start work at 7 go to lunch at 12) it cranks for 3 or so seconds before starting. Any ideas why?