UPDATE: Apparently car only overheats during city driving. Pressure tested after heating car up. Quickly lost 5 psi with no visible signs of leakage or signs of coolant appearing externally.
After some research it was found that the car uses a 3 layer head gasket to individually regulate cylinder temperatures. The center layer can shift causing incorrect distribution of coolant and improper cylinder temperatures.
Customer authorized the head gasket job. I pulled the head off last night and the head is currently at the machine shop being cut and pressure tested for cracks. Cylinder 1 had twice the amount of carbon as the others cylinders, even through the intake port. This could indicate that this cylinder has been running at a different temperature than the other cylinders.
I will post again with the results after the car is put back together.