1999 Chevy Blazer Blazer will not start

I have a 1999 Chevy blazer 4.3 L V6 vortex. My truck has been working but sometimes when I stop it will put before it will go good. I went to Maryland last month left my car at the fire dept, when I got home it would not start. I replaced the spark plugs and everything was fine until today. I responded to a fire call last night everything worked fine after the call I came home parked the truck went to bed got up for a fire call the next morning and it would not start it has spark, fuel pump works, and timing works it is TDC. Grate fuel pressure when I turn the car over it it just turns and when I let off the key it puts but doesn't start