Hi, My name is ***** ***** for the delay.
I will do my best to assist you
if it is going as if it gos into neutral when it is time to shift,the problem is still the transmission,the 3-4 clutches is what burns out of these 4l60e transmissions that will cause this.
if you have replaced it with a new rebuilt unit,take it back and get another,
i would advise against buying a used 4l60e,sense it may also be worn and not last long.
sorry,but the problem seems mechanical and not eectrical,the transmission will need to be rebuilt or replaced,sorry
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