Comes back and stock tiers
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Hmm. I don't understand how these codes could be set and not produce an ABS light in the cluster.
Your best bet at this point is to get someone with a GM Tech 2 scanner that can read the individual left/right front wheel sensors and verify they are operational. GM dealer can do it as well. Alternately, you could just try replacing both front wheel sensors, but check the ABS module ground as I mentioned above, that's a $0 cost thing to try first.
If the truck has been flashed with a tune, that's another source of potential problems if the incorrect calibration was used. Flash it back to the stock tune, clear the codes and see what happens.