some devilles came with the 4t60e which is pretty close to the 65. my 99 grand prix wont shift from 2-3. i can keeping accelerating and hit about 45mph than it will shift into OD. if i cruise at 55mph or so and punch it, it willl downshift into 3rd and stay there as long as i give it 2/3 gas. once i let off the gas it goes back to OD. so, no 3rd on upshift but i can make it go into 3rd on the downshift. so 3rd gear is THERE. i have a cel for emissions stuff. had it on/off for years. comes and goes. have not checked recent codes. not even sure if a cheap code reader will pickup and trans codes. ya i know. 99gt. 150k miles. time for rebuild.