Just curious does the whole front of the car drop when you put it in gear and it dies? This may sound crazy but a few years back I installed a brand new TCI trans and
converter and when I started the car it ran great and I had it on jack stands for the initial run through the gears and it seemed find and then we dropped it down and tried to go for test drive and as soon as I put it in 1st gear the nose dropped and the car chugged out, after many theories we figured it out....it was the converter, not sure exactly what was wrong with it but it locked up as soon as it went into gear, changed it and that was that! So if you cant figure it out electrically or otherwise check the converter.