1999 Chevy Suburban C1500 starts in cold weather but not in hot/warm weather.

I have a 1999 chevy suburban c1500 with a v8 vortex 5.7 engine. Now the problem is that it has a very hard time starting, it cranks, but again will not start. After I have cranked it several times, it starts up slowly, puttering itself to life. It idles rough for 15 or so min and then runs ok. When the engine temp is up and I run it all day, it runs fine. I can turn it off for a couple of hours and it will start up. It seems that if I don't use it for more than 12 or more hours and don't use it until the next day, it won't start. Now the funny thing is it turns on when its cold outside but not when the weather is hot/warm. I have replaced the fuel pump, distributor cap and rotor, cam and crankshaft sensors, spark plugs and wires. I don't no where else to start. I have researched the internet for answers and people has suggested the fuel pressure regulator. Would like to make sure before I spend my life taking the intake manifold assembly apart. Thanks.