pulsing vibration???? WTF
If you rev up in neutral does it still do it?
Maybe engine/tranny mounts worn? driveshaft?
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Tho, one of the the stock stall converter bolts had broken off (apparently before i bought the car). There was a hole in the shield where it had shot itself out. Im guessing this aided in the destruction of something else, causing the vibration.
swap and I think it's some kind of internal imbalance in the
free-spinning parts (since lockup makes it quit).
i took it to an exhaust shop and had my exhaust slightly adjusted. it turns out, my exhaust was rattling and tapping the floorboards or something. there was a nice little mark on the I-pipe where it had been constantly hitting. it has to do with these cars - at 50 miles per hour, the frequency emitted either from the exhaust or road vibrations at that exact RPM sends a ripple throughout the car that causes everything to rattle. this is how earthquakes knock down buildings - when the frequency of the earthquake matches the building's natural frequency, it shakes violently and falls apart. when the vibrations in the car at a certain RPM reach your car's natural frequency, things start rattling. the extra clearance from the adjustment stopped the rattling.
get your exhaust adjusted. that may fix it. FWIW, my car did this the WORST when WET. it was horrible in the rain. it hasn't happened since the exhaust adjustment.

