I did all the air checks and they were good. I did check the front servo and didn't have pressure, but the service manual shows it has to shift into 3rd to have pressure there.
The front servo is applied when the car shifts into 2nd gear. That is what applies the 2nd gear band and stops the sunshell and direct drum from spinning. It shouldn’t have pressure in first or third but in second it should have pressure. Since yours won’t shift to 2nd, it sounds governor or valve body related. Only reason I asked about the pressure of the front servo is because if it was seeing pressure but the car wasn’t shifting, then there could have been a broken band lever, band tab, broken strut. So since there’s no pressure, that confirms it’s not shifting, opposed to it’s trying to shift but the band hasn’t been applied via the servo.
Give update after you check governor pressure and line pressure. I’m not super familiar with the trans go kits as I don’t use them, but I know if anything is not correct in a valve body, the trans will do crazy things.