not too hard... biggest PITA is getting the glass in and out of the track without breaking it.
actually... removing the regulator assembly from the door can be fun too.... it has to be in the right position to come out of the hole
Start on the donor truck: remove the door panel, then remove the vent window (3 screws on top, 2 bolts down low, 1 screw just below the window) then you can get the main piece of glass out, finally pull out the regulator. Then repeat with main truck, then reinstall in reverse order.