TRANS GOES TO LIMP MODE WHEN SHIFTING INTO THIRD GEAR

[MOJO]

I HAVE A 99 SILVERADO THAT FLAGS A PO758 2/3 SHIFT SOLENIOD ELECTRICAL CODE. HAVE REPLACED 1/2 & 2/3 SHIFT SOLENIODS AND TRANS WIRING HARNESS ALSO SPEED SENSOR. CAN CLEAR CODE, START TEST DRIVE 1/2 SHIFT GOOD 2/3 GOOD THEN INSTANLY DTC APPEARS AND GOES INTO LIMP MODE. THERE IS NO DATA FOR TRANSMIISON READING ON SCANNER AT ANY TIME. ENGINE DATA IS ALL THERE AT ALL TIMES. SCANNER DOES HAVE THE CAPIBILITY TO CONTROL TRANS SHIFTS AT MY COMMAND. IF I STOP AND START TEST DRIVE IN COMMAND MODE THE TRANS WILL SHIFT UP AND DOWN WITH COMMANDS.THE FAILURE CODE DOES COME ON WITH 2/ 3 SHIFT COMMAND IN THIS MODE BUT WILL NOT EFFECT THE ABILITY TO SHIFT TRANS WITH SCAN TOOL IN COMMAND MODE. HAVE CHECKED AND RECHECKED POWER ON FUSES, POWER AND GROUND AT THE DATA CONNECTOR {GOOD}.

[ProTech]

Check the wiring at the connector on the transmission. There have been some known issues in that area. Also you might want to trace the wiring from the connector back up through the harness for any corrosion, chaffing, etc. If nothing checks out in that area, you could be looking at a faulty PCM, or something else wrong inside the transmission.

[MOJO]

(OHM) POWER WIRE AND 1-2 AN 2-3 SOLENIOD SIGNAL WIRES BETWEEN TRANS CONNECTOR AND PCM CONNECTORS. ALL GOOD. TOOK TO LOCAL CHEVY DEALER AND REQUEST ORIGINAL PCM TO BE REFLASHED. PCM FAILED AND WOULD NOT RE-FLASH. PURCHASED USED PCM FROM LOCAL SALVAGE YARD. DEALER INSTALLED PCM AND RE-FLASHED IT. TRUCK HAS DRIVEN WITHOUT FAILURES FOR A COUPLE DAYS.

[ProTech]

Looks like the PCM fixed your issue so far, which I suspected would be the problem if you didn't find any wiring issues. Glad to help!

And from now on, PLEASE do NOT use ALL CAPS in your posts!