Hello and welcome to just answer,
These can be a pain to remove, GM makes a hinge pin removal tool kit for these, the kit is very costly. It is a large "c-clamp" type press with adapters.
I have found an aftermarket tool made by eastwood tool, http://www.eastwoodco.com/jump.jsp?itemID=1689&itemType=PRODUCT
I have never used this one but it looks like it might work its $35 bucks versus the GM kent moore at $800 bucks.
let me know if you have more questions