Wait..gas AND water in the oil?
Cylinder location is the same for the 3.1
Standing at the front of the car, look towards the rear.
3.1 V6, the order is:
Firewall, left to right
1 3 5
2 4 6
Radiator, left to right
Coil packs are, left to right, 1/4, 6/3, 2/5
I don't have The Book with me right now for the DTC, but if a GM dealer hasn't heard of it, make sure you wrote the code down right.