Lock up torque converter won’t unlock

The reason I’m putting this post in the general discussion part is I’m not sure if it’s a transmission issue , computer issue or a chip issue. Last week while doing a shake down drive my car would stall when coming to a complete stop. This didn’t happen right away but only after about 8-10 miles. Wasn’t beating on it, never more than 1/2 to 3/4 throttle. Just prior to the drive I replaced radiator and thermostat. I re set TV cable and changed trans filter (was having issues not shifting out of 1st TV cable was the issue). I have replaced the TCC solenoid and adjusted linkage but my stalling problem still exists. Now for the computer part of this. My scanmaster says it’s in park/neutral when it is in park neutral and says drive when it’s in drive but next to the “trans” it always says 3rd. Could /would that be causing my transmission issue. I’m 100% positive my stalling is from the trans issue not fuel


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the 3rd gear switch is not likely the cause of your issue. You said you replaced the TCC solenoid, which was my first guess.
if your foot is on the brake, the electrical feed to the TCC is interrupted, so the computer can't lock the TCC.
It's easy to short the wiring to the TCC when changing the filter or TCC itself. If shorted inside the transmission to metal the lockup will occur all the time you don't have your foot on the brake pedal which opens the +12 part of the circuit, as mentioned by Bob.
Unplug the connector on the transmission and check for +12 and GND on it KEY OFF test.
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With the connector unplugged check Pin D the tan/black wire for a short to ground with an OHMMETER or test lamp.
KEY OFF test.
If grounded on the harness side the wiring is shorted or the ECM is shorted and bad. Further testing needed.
If it is not shorted to ground the wiring insulation inside the transmission is sliced and shorted to some metal (also ground).
Or the TCC itself is bad which is rare.

You won't be able to test the +12 on the connector (unplugged) with a KEY OFF test but since it's locking up all the time you already have that +12 on the purple wire working. The issue is the TCC tan/black wire being grounded somewhere usually it's inside the tranny.