Hi,
These vehicles are controlled by different computers/modules. The idea that a different model transmission was used leaves me with a lot of questions. Do you know if the transmission was from the same year make and model? By chance, do you know the model number of the replacement computer?
When you place the transmission in park or neutral, does the gear indicator show the correct gear?
If this truck has a 4.3L V6, the PNP (Park Neutral Position) switch is on the left rear of the transmission and not internal. The PNP is part of the range sensor and backup lamp circuit.
Also, let me know if you tried starting it in neutral.
Take care,
Joe
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Wednesday, December 15th, 2021 AT 8:12 PM