It seems that people do various amount of renewal of the Sierra rear drive shafts. Some do none, some do a full rebuild, including sandblasting and new bearings and gaters. The gaters on mine definitely need replacing. On top of this I've opted to dismantle the hub carrier and replace the bearings and oil seals. This was not essential, but I would have not have been completely happy if I had ignored them. There was a lot of dirt where the drive shaft enters the hub carrier and I would never have been able to fully clean it. Also, while the bearings did not appear to have any play in them, but they were far from running completely smoothly.
How to get them apart? We'll I tried a 41mm 1/2 inch impact socket with a breaker bar, with the drive shaft mounted in a WorkMate. No joy. Tried the same, but with an air powered impact wrench. Still no joy. Yes, I did remember that one has a reversed thread and copious amounts of WD-40 had already been applied! This is all quite straight forward on the original Sierra as you can apply the car's handbrake and the drive shaft is not going anywhere. Much more difficult off the car.
My next solution was to try holding the drive shaft with a long metal bar with a hole drilled near to one end for one of the wheel studs and using a breaker bar to pull against it. Instant success. With the hub carrier and driveshaft separated it was then a very easy job to remove the bearings and oils seals. The bearings and oil seals were kept for reference and the remainder of the parts cleaned of grease and dirt, ready for rebuilding later.