aaarrrrrgg 5.7 vortec wont start again!!!!!!!

[old Chevy guy]

I have an 01 3500 box truck with a 5.7 vortec,a couple of monthes ago it had a starting issue that I thought was related to timeing. The timeing has been set but since then every time the truck sits for 4 days or more without being started it wont run.I now think the timeing althou off was not the problem why it wouldnt start then.It seemes to be getting fuel,in fact after trying to start it it even smelled flooded.I know this is probly from trying to start and the injector dumping fuel.When it finnaly started the other times it always acted like it was flooded,you know black exaust,rough then clearing up.I dont know if it didnt start because it was flooded or if it got flooded cause it wouldnt start.Why only after 4 days? If I start it ever day or even every other day no problems ,and always runs great when it starts.I borrowed a fuel presure gauge and will check that in the morning.Any suggestions are welcome.Someone suggested the fuel presure regulater?Anyone think that could be the problem?