If you had corrosion at the battery cable bolts then you probably fixed it. Moderate to heavy corrosion at the cable could present just like a bad starter

 

Corrosion at the battery terminals wasn't that bad, i had replaced the to mounting bolts that attach to the battery a couple of months back. However at the junction box, both positive and ground didn't look so hot, and neither did the ground attached to the frame.

 

Just replaced the starter on my '02 Yukon...I think it is the same as your rig. I cheaped out for the REMY remanufactured starter from RockAuto for 100 bucks.

I don't think there is any way to disconnect the wires to the starter prior to removing the starter from the bell housing. One trick that I lost time on was to cut the cable tie wraps that hold the starter cable to the frame. I muscled the starter for an hour before I figured that out. Also, you can remove the heat shield on TOP of the starter (around the solenoid) before you drop the old starter...that will help...and wait until the starter is completely installed before you snap that heat shield back into place.

Good luck...

 

Thanks I appreciate the the info.