Long Crank No Start
 

I have a 96 7.3, Rebuilt engine 3 years/20,000 miles ago. I have done regular services on it since the rebuild (oil, oil filter, fuel filter). Been having starting issues last couple months. Replaced glow plugs, G.P.R., C.P.S., checked the oil pressure sensor for the injectors and have plugged it in overnight to try and figure a remedy for long cranking and lots of white smoke. I know white smoke is unburned fuel. Will crank for 15 second intervals and takes anywhere from 3-4 cranking cycles before vehicle will start. Lots of white smoke while cranking and even more when truck finally starts. When it starts is seems to run just fine, minor amount of blue smoke at idle which goes away after driving a couple blocks. Vehicle uses minimal amount of oil. Been looking on all the forums for answers for long crank and white smoke and I have changed everything that has been suggested and problem still exists. Problem only happens in the morning after sitting overnight. I have had my truck sit all weekend from Friday after work till Saturday or Sunday evening and it starts after cranking for just a few seconds, but still has white smoke. Any information or direction would be awesome. Truck ran awesome after rebuild and still does once it is started and warmed up. The only thing I haven't done is start vehicle with valve covers off and check for bad injector o rings. That is going to be my next step unless I am told otherwise.