So let's start with the ill-effects of cold weather. When temperatures drop, several things happen that can make a diesel hard to start. First, the oil in the crankcase thickens. At the same time, battery output drops, reducing the number of amps available to crank the engine.
Examination should always begin with which objective lenses
Outside temp is 97 degrees. Vehicle does have fuel as I added 2 more gallons just to make sure it wasn't a stuck gauge. This is a 1986 M998 with a 6.2L that ran perfectly yesterday. There are three other occasions when trying to start the vehicle it took approximately 15-20 seconds of cranking the engine before it would start.