My 4L80e will not shift out of 1st gear. I'm sure it's not 2nd, and I'm sure it's not in limp mode. No codes. Using a trans-specific .adx, I see 0 mph vehicle speed while driving. Everything else seems to register. But the weird thing is, and the reason I say "sort of" in the title, is if I use my typical engine .adx, speed registers normally. I can't figure this out. Why would one .adx show speed and the other won't? I have previous data logs using the trans .adx and they DO show speed and of course trans shifted normally.

Here's what I've done so far:

- made sure VSSB is getting key-on 12v and ground to it is good.
- tested continuity on twisted pair wires that go from t-case VSS to VSSB. All good
- tested continuity on both wires that go between VSSB and 7427 PCM. C11 on VSSB to F13 on PCM - good. C13 on VSSB to F12 on PCM - good.
- Swapped to a backup 7427 PCM - no change. Note that I only have one MEMCAL, however. Had to use this same MEMCAL in both PCMs.

Possible suspects:

- VSSB is bad.
- Bad connection somewhere between VSS, VSSB, and PCM.
- MEMCAL is bad.
- Bad ground somewhere
- Something else I'm not thinking of

Backstory and disclaimers

- This came after valve lifter and intake manifold replacement. Of course I had everything on top of the engine off and disconnected. I was going to swap to Vortec CSFI multiport, but I ran into too many challenges and put that project on hold. Went back with everything same as before. (46 mm TBI, 454 injectors. Engine is a 383, vortec heads)

- I have both the original 1991 DRAC and a VSSB from a '94 truck. DRAC runs the speedo only. (speedo working fine) VSSB provides both outputs to the PCM. (40 PPR and 2K PPM). There are two twisted pairs connected at the t-case VSS - one goes to DRAC, the other goes to VSSB. This set up worked fine for months before the lifter replacement. One thing I'm considering is eliminating the original DRAC and using the VSSB to run the speedo. Eliminate the second feed from the VSS and use the original feed - rerouting from DRAC to VSS.

- '93 and older 4wd with 4L80e used 3 VSS: trans input, trans output, and t-case. When I switched to 7427, this eliminated the need for the trans output sensor. The sensor and wiring is still there, just not connected to the PCM. Again, everything worked fine before the lifter replacement.

- I've also been messing around with the original vacuum modulated cruise control. As in eliminating it and swapping to electric cruise from a GMT 400. I've been tracing wires under the dash, but haven't cut into anything. I can't see how this would cause my problem, but need to mention it since I've been under there in the time frame from when everything worked to now.