I'm working on a friend's 6.0. Truck has codes for glow plug circuit on cylinders 5, 2, 4, 6, and 8. So far I've tested the glow plugs and all of them ohm out at 5.6- 5.7 except one at 57 ohms. Last week I changed out #4 because it was at 51 ohms. At the time #4 was the only code. Pulled the...