Is that 2.5 inches, or mm?
Tool change position is always in Machine Coordinates. Park position gives you the option of using Machine Coordinates. I highly recommend that you do so (with the checkbox).
Do you have a Z axis home switch at the top of the Z axis travel?
After homing, what is the Z axis position in Machine Coordinates?
When you home the machine, it should set the Z axis machine coordinates to zero. Z- is down, so the tool change position needs to be less than zero. But it also need to be higher than where you zero the Z axis, in Machine Coordinates.
After you auto zero, what is the Z axis Machine Coordinate, and what is your Clearance Plane setting?