I can't figure out whats going on with this TPMS system. Help!

On startup, the yellow dash light blinks, there's a chime, and the EVIC says Check TPM System

The EVIC in the TPM mode shows "--" for each of the 4 tires. Every 10 minutes of driving, the blinking yellow dash light returns for a minute.

Using a DRBIII to scan the SKIM module, the DTCs are "Transmit Failure" for all 4 tires. They are new Dorman sensors last year. Tonight, I replaced all 4 with new Standard brand sensors. Same.

Also using the DRBIII:

Reading TPMS sensors shows 0.0PSI for 1-4 and 32.PSI for tire #5.
I can program a different sensor ID for #5, but 1-4 IDs are all zeros, and I cannot program IDs for 1-4. I can change the ID for 5 only.
There is a TPMS read test that has to be done at 20 MPH or more for over 75 seconds. This results in a failed test to read 4 sensors.

So, it seems like it's reading the spare, and no others. How is this? I know there's 3 wheel well sensors, leaving the left rear without a sensor. How is that wheel read? Same as the spare?

Where do I head next in trying to troubleshoot this system?

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06 KJ Limited CRD
mod airbox
EHM
Mishimoto hoses
Weeks Stage1+2
Yeti stage 2 ECM
GDE ECO TCM
FTC billet TC
Transgo kit
no mech fan
Cummins lift pump
2.5" catback
OME 790/948 springs
JBA top plate and UCAs
2 upper rear insulators
Bilstein 24-139168 front 24-186704 rear
255/70R16
1.25" wheelspacers
SkidRow engine plate