Every morning I have dry crusty gunk in the back of my throat, why?  

Rhinitis or GERD. This may from several things - 1) if you snore... Your mouth is open and the back of the throat (and mouth) can dry out... Very common complaint in snoring and sleep apnea. 2) this could be nasal drainage (rhinitis) (allergy or non-allergy related). 3) this could be a manifestation of acid reflux (gerd).
Dry throat. Hello, the "gunk" you are describing is a dried out mucus that comes from the evaporation of the moisture while you sleep. If you are also a snorer, you may have a condition called sleep apnea. These patients often have the same dried throat in the am. Drinking water, sleeping with a humidifier may help. If you have sleep problems with witnessed stoppages of your breathing, see your doctor.