LSx wiring; communicating with PCM

I'm in the home stretch on the 5.3 swap into the Henry J. I've modified the harness according to internet wisdom and factory service manuals but I still can't talk to the PCM through my HPTuners software or my generic code reader. The code reader does power up though, so that makes me think the power and ground circuits are fine.

I've got the pin #58 from the blue connector going to my data line on the DLC connector. Engine is from a 2004 Trailblazer, running electric throttle, AC and all the goodies.

The plan for today is to grab a second set of PCM connectors from the junkyard and de-pin everything that isn't power, ground or DLC connected and make a mini-harness just for flashing the PCM to make sure that the PCM I have is good.

Any other ideas where I may have gone wrong in my wiring?

I bet you don't have your communication wires hooked up correctly. You need 4 things at the dlc, power, ground, and both communication wires.

I've tried it with both ways, both com wires to the DLC and with both the grounds tied together like some of the swaps I've seen, but that's what I was thinking. I'll get some time to play with it tonight after my day as a Ford tech.

I had to move one of the communication wires in my OBD-II port for one of the LS swaps. Can't remember the details other than reading the wiring diagrams told the tale.

Just a follow up in case anyone runs into similar problems:

I double and triple checked the wiring, it passed a visual and resistance check with the meter. My bench harness worked for reflashing the PCM with my HPTuners so I plugged the PCM back into the car and it fired right up and idled nicely. I'm using drive by wire and it was intermittently working and kept throwing codes for the circuits to the gas pedal sensor. The wires to the sensor checked out OK so we put a new pedal/sensor in it (The thinking being that with the hard hit the donor had taken the snsor may have been damaged by the driver's weight suddenly smashing into the pedal)There was no change from the new pedal when I was told that the TAC module (controls the electronic Throttle Body)had been picked up out of a mud puddle near the donor. I unplugged the TAC module and turned it upside down and watched several tablespoons of water drain from it. The TAC module spent a night in a bag of rice (which is a great desiccant, I used it on gameboys and cell phones before it's always worked)was put back in the car the next day and now I have no more communication or gas pedal problems.

Makes sense, the DLC basically works by making the scantool a module on the data bus, the TAC talks to the PCM on the same data bus, so a flaky TAC can take out the data bus which means no communication via the DLC.