Alright update time:
Put in the new speedometer cable, still didnt work. looked closer to the mechanical sensor, and saw that the bolt which mounts the sensor in was gone (as in...I forgot to put it back in when I did my VE swap) - The unit wasn't out of its housing, so it shouldn't have made a difference...but hey, I've seen stupider things happen. Went to my bolt bucket (from 3 dead partouts!) and found the correct bolt, popped it in, and badda bing! works. Go figure.