Little more info on the whole 5.3L.
From a 2004 Tahoe with only 1400 miles.
The guy I purchased this 5.3L from bought it from a 4x4shop in Siloam Springs, AR.
I was told they reprogrammed the ECM, modified the wiring harness down to a 5 wire hookup.

List of those wires and what their for:
brown = Alt. light or gauge
pink = key hot (must maintain 12v while cranking)
green= battery (hot at all times)
white = tach
purple = starter

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I know it is not the MAF sensor.

It does have 4 wires.

left to right in picture
I beleive them to be:
orange, purple, brown, pink.

The drive by has been replaced for a cable throttle.
I would assume that when the harness was reworked that they would have removed the wiring for the drive by. But I know what assuming gets you.

it is the plug hanging to the bottom left in picture
(MAF is the one hanging bottom right)