If the starter is dragging, it could be a couple of things - but I agree that the place to start is the ground side.

Disconnect the battery. Remove the bolts holding the ground cable to the inner fender and frame and remove the ground wire do you can see it. Examine it for corrosion. If it looks ok, clean the terminals, the area around the frame and fender bolt holes and the bolts with a wire brush and/or snadpaper and resinstall it. Before you connect the battery, clean the battery terminals (on the battery and the cable clamps) with a battery terminal brush and the (+) wire (big one) at the starter. There's another ground cable on the driver side from the inner fender to the frame - clean that one too. If that doesn't fix it, you probably need new battery cables or starter brushes.

Frank