I have hit the point where I cannot find any decent information for troubleshooting this condition. For starters, truck had a major tune-up less than 10K miles ago. It is a 99 5.0L (Sierra Classic), I have removed and cleaned the CSFI unit, and it did have a sticking poppet on the #4. The regulator appears to be sound (no leaks), and I can find no evidence of any other leaks. The fuel pump will pop up to 64lb, though it falls off quickly since I have not figured a safe way to close off the return line. When the #4 poppet was stuck open, the fuel pump would not pass 56lb. I replaced all the gaskets as well. First thing in the morning, the truck will fire up like it always did, within 1sec of cranking. After the truck has warmed up however, it is very hard to start (5-15sec), and I have to open the throttle plate to get it to idle. After it is started, it will miss and hesitate until I tap the throttle, after which point it runs just fine. I am starting to wonder if this starting problem could be sensor/actuator related, possibly involving the TPS, IAC or either the coolant TEMP or intake TEMP sensors. I thoroughly cleaned the throttle body and the intake. I do really love the o-ring style gaskets, no mess, no fuss. I was initially concerned that the engine was starting like it was flooded after it was warmed up, but I am not finding any evidence of further leaks inside the manifold, though it is a bit harder to tell since I went and cleaned it. Shouldn't have done that. AC Delco is recommending that the CSFI units be converted to Mulit-Port units, but I don't want to replace anything more than I have to. Has anyone else succesfully dealt with this symptom? I have seen many references to people with the same issue, but no resolution beyond shotgun replacement of everything. Any thoughts/techniques welcome.