99 cummins turns over to slow to start
 

I went to start my dodge this morning, but it turned over to slow to start after pre heater said it was ready to start. I charged the battries and had the same problem. I took the batteries to be tested and was told that they were fully charged. The engine still turns over slowly like it has an almost dead battery. Is it my starter?

buy a starter, or rebuild the one you got