Running a bbc rod, art Carr built the 2004r and so far it’s held up great but it is changed over to non lockup , at the track I shift around 58-6000. Putzing around town I usually shift about 52-5500Yeah, it sounds very potent, probably pushing 600 ft/lbs. Your 455 was obviously built right, not so easy as many have bottom end issues. Stock rods? What rpm are you shifting at? I am betting you are flashing past the 3400 rpm rating on your converter. Who built your 2004R? Still, the 8.5" should have held but obviously didn't. This is why people love the Olds 455 because it can break pretty heavy duty components with its torque. All around a very nice car.