Just went out and verified, and as I suspected, whatever you're reading in GNTTYPE is in error.
It is the purple/white wire. The reason you see the designation C1-3 is because the two connectors are labled C2 (small one) and C1 (larger one) in some factory documentation... In other docuementation (service manual I think), you'll see them designated A or B or C or D with pin numbers.
Here's how they're layed out. The small connector (on what I call the south end of the ECM) is C2, but has two rows of wires labeled row A (on the latch side) and row B (opposite from latch side).
The large connector (on what I call the north end of the ECM) is C1, and it's two rows of pins are row C (on the latch side) and row D (opposite from latch side).
So, armed with that info, you'll see how easy it is to find D3 (boost solenoid control) purple/white. It's on the large connector, on the D side(away from latch) closer to the "south" end(end away from fire wall).
Hope that helps.
CAUTION: make sure you hook the BstC brown wire to the cut purple/white coming out of the ECM, and the white wire to the cut purple/white wire going out into the engine bay.