I've been though just about everything on my '99 4.3 Vortec, except injectors, but they test okay. I do have a small leak I think on the FPR. It leaks down kinda slow.
I think on my case it's actually fuel related because when it's done it lately I've been able to start it after pressing the gas pedal all the way down, but it takes like "forever" cranking, maybe 2 minutes. Enough to be on the verge of smoking the starter.
My '00 K3500 5.7 does not have this problem. I replaced the injectors because one was faulty and realized the distributor cap was cracked, and it looked original! I was going to immediately replace it, but was too afraid if I was going to start having these problems on it too.
I was going to respond on the other thread and the guy constantly asking if SBC is more "reliable" than his wife's LS-based 5.3...but got sidetracked.
Um, well most engines seem to have common issues, and this is definitely one of them on these engines. However, I thought it was just the 4.3s.
I had to go to Rockport to look at some building with Hurricane Harvey damage a few years back. The morning I was supposed to leave damn truck didn't want to start. Humid morning. Finally got it started. Can't drive across the state with that uncertainty.