4L80 swap going into limp mode after 1-2 shift
 

0x10: P0758 - Shift Solenoid B Electrical (Pending, Current, History)

2001 GMC 5.3/4l80, cam, bolt ons.

Did the swap and the Relay mod, Transmission worked fine for about 2 weeks and started going to neutral when trying to shift into 3rd. Pulled the main connector and transmission still defaults to 3rd so i dont think its a hyd issue.

I have checked and triple checked the wiring, replaced the relay, checked the pins in the main connector on the trans, checked the pins on the harness on the transmission, checked the harness from the pin in the ecm to the transmission.
Only thing i haven't done yet is Ohm out the 2-3 solenoid

The conditions for the code to be set:

The PCM commands the 2-3 SS valve ON, and the voltage input remains high (B+).
The PCM commands the 2-3 SS valve OFF, and the voltage input remains low (0 volts).

Im at a loss. Anyone have any experience with this issue?

i'm having similar problems. not sure if mine is wiring or solenoids yet, but i did rule out the trans segment swap as it shifts my other 4l80e just fine.

excuse my ignorance what is the relay mod?

It keeps you from having to do a segment swap. I plan on digging into it more this weekend to see if I can figure it out.