I have a 2001 silverado 4x4 with the 5.3 V-8 that is hard to start some times. Changed out fuel-pressure regulator, helped some then checked pressure on rail and was fine so pump must be ok. Also changed out fuel filter. There was a service bulletin about sulfer buildup on fuel pump and to use gm fuel cleaner in gas. Has anyone else had this problem? I bought the truck new and plan on keeping it a while, only have 64,000 miles on it.