Okay, I thought long and hard and it finally dawned on me, The GG1s most definitely pulled at least one unit train on a semi-regular basis. A very well known unit train. The twice-weekly, 60 car long, insulated boxcar Tropicana Orange Juice train.
It's original terminal was at Meadows Yard in Kearney.
The train was regularly handled by GG1s, E44s or sometimes a combination of both types of motors.