I have a 05 GTO and lately it has a intermittent cranking problem where it turns over slowly and irregularly. Sometimes it cranks fine, sometimes it cranks slower and sometimes it cranks at a medium speed. The battery is a (newer) deep cycle marine battery. I took the car to advanced auto and had them check the battery, starter and alternator and they all came up clean. I did clean the battery terminals but it didn't help at all...any ideas?