2003 S-10 pinion seal leak

I have a 2003 Chevy S-10 4 door 4X4 with a 4.3 liter engine. It has almost 52000 miles. Automatic Transmission was rebuilt at 35,000 under warranty.
I need to replace the rear pinion seal, it leaks. After taking off the drive shaft and marking and taking off the large nut I guess on the differential, I can't seem to dislodge the part the drive shaft connects to. I called many people and they say pound it off, but I can't. I pounded and pried for hours and still can budge it. Do I need a certain type of puller? And if I do, what exactly do I ask for? I heard it might be called a differential yolk puller?