gmguy, I'm assuming the GMC is the same as the Chevy set-up.
Go to the very rear of each slide and put your hand down the back of the floor support,you will feel 2 of 1/2" nuts, they might need some spray to free them up.
There's 2 on each side.
At the front of the slides they simply bolt through the support that's welded to the floor.Again 2 1/2" nuts per side.
You should then be able to lift the complete seat and slider assembly out.
The slides will remain attached to the seat frame.
Get some one to give you a hand,it's awkward and heavy!
