This is the tool you need. It's model 25112. Worked on my 99 Yukon. I searched this thread a few weeks ago and didn't see it mentioned. It's $50 on Amazon. I tried the silver looking one that looks like a jaw, those didn't open wide enough.
The nut on the end of the thread comes off, if you take that off the bolt and leave the castle nut on a few threads the bolt will go up into the nut and help hold it in place. With the nut on the tool it wants to slide off the castle nut.
I replaced ball joints few weeks ago and could not get the ball joint to separate from the knuckle with a pickle fork or hammer. This makes it a lot easier. You might need to cut the boot on the old ball joint to help it fit in place. Then start turning the bolt on the tool. If it is still stubborn you can try just leaving the tool on for a bit. When I removed the second ball joint, I tightened it down and got tired and stopped for a minute, and then the thing suddenly POPPED and broke it loose.
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