The TH350 from the 70's was not bullet proof. Had one die in our old family 75 Cutlass 4dr. Also my nice shape 76 Cutlass 2dr. It was parked due to the TH350 heading south. I heard rumors of whale oil being removed from ATF causing issues a few years back. The shift timing is either governor or modulator. My TH350C that was less than great also shifted too early. A different modulator helped the awful lugging a bit. Of course dumping that turd of a sbc 350 for an Olds 307 was even better.