Speed Sensor vs. ABS sensor.

What is your question?

I went to Advanced autoparts store to get replacement sensor for the one ontop of the differential. They had 2 different ones that were identical in looks. One was an ABS sensor the other a speed sensor. I was replacing it because my speedometer flutters and the abs light was on, it would downshit hard sometimes in bewteen 2nd-3rd gears. Does anyone know which is the correct for a 94 E350 RV with a 460 gas engine and automatic trans with OD?