Turn key 1 click won't start
I took my truck to a GM Certified Mechanic. They
had it over 8 hours, couldn't find anything wrong
with it. Back up to Sunday I went to start it and it
just clicked 1 time wouldn't start, eventually it
started(reason I took it to GM dealership). Drive it
home from dealership today ran great, took my
daughter to softball practice, wouldn't start, just 1
click and nothing. Sat there 2 1/2 hours, it started
no problem. Dealership says nothing electrical,
battery is perfect, starter is great, no corrosion or
corroded wires. What are they missing