What do your cables look like? I've had some that looked decent. It when you cut them they were a mess inside. Replace the cables and clean the ground good. Also make sure all of the wiring is decent so that the coil will get as much juice as it can when the starter is pulling lots of juice away. Start at the battery and clean everything all the way out.
Are you sure the battery is good? It may be able to hold a charge but can't stand the load of the starter.