I just joined this forum because of this same problem... I have a 2000 Silverado 5.3 and have had this hard starting problem for about a year now. Sometimes it would start right up and other times take a while. Also have had to pump the gas pedal at least once, while turning the key to get it to start. I have replaced the fuel filter, air filter, air Idle control valve and was thinking about replacing the fuel pump... I only have about 64 K miles on it and I am hoping that this is my problem. Auto zone is closed right now but if they are open tomorrow, I am going first thing in the morning even though it is a holiday. Can not wait to see if this will fix it. It's been driving me crazy!!! Ill keep you all posted... Thanks for the help!!!
Good news and Bad news!!! The good news is that my truck now starts right up every time. Sure enough it was a bad fuel regulator... I had fuel in the vacume line. Now for the bad news... For some reason now my truck is backfiring and sometimes i get a little hesitation. The backfiring mostly happens when I slow down around 15 -25 mph then hit the gas to accelerate again... Not sure if this has anything to do with the lucas injector cleaner that I am running in my gas. This has never happened before and its not the first time ive used injector cleaner. Also for some reason when slowing down at a stop my idle sometimes goes down to about 2000 rpm and the truck sounds like it wants to die. Not sure if I have a clogged injector, bad o2 sensor, or maybe now my idle sensor is bad. I took the Throttle Body off today and cleaned it very good. I also cleaned my battery cables and retightened them today and I am still backfiring. Now Ive changed the fuel regulator, the fuel filter, the air fiter, and the air idle control valve. I was thinking of changing the idle sensor that is located right under the air idle control valve next.