[Bully]

2003 Duramax diesel
Truck has run flawlessly. Late last week, noticed that rather than starting after turning over 5 or 6 times, it seemed to be dragging on a bit. No real problem after starting truck ran fine, pulled hard, no stumbling or smoke at all.
Saturday am, truck spun over and over, no sign of starting. Checked pressure at fuel filter, all good. Turned it over again, stabbed the throttle a few times, then held it to the floor, started right up. Then same story ran fine, no issues.
I figured maybe glow plugs, get a diesel mechanic buddy to scope the truck, and nothing wrong, and of course since Saturday morning truck has fired instantly and run fine.
I hate the thought of mystery issues.
Any wisdom from the brain trust????