might have wrong converter. There is one with a bushing in teh stator and one with a bearing in the converter. Mismatch it one way and it wont go in. Mismatch it the other way and you get a TCC code.
Your code definition is off. P0740 means TCC slip NOT " torque converter lockup open circuit". There is a big difference in the diagnostic process between a solenoid "open circuit" code and a TCC slip code. The meaning of the two codes is extemely different. Some OBDII definitions are "screwy" and could lead to misdiagnosis like trying a harness when its not an electrical issue.
If you drive the car with vag-com hooked up you can watch and graph TCC slip. This wont tell you what is causing it, just that its slipping which you know allready since you have the code.