2006 Dodge Ram 3500 diesel not starting

[jallison]

Hello to everyone, i have an 06' ram 3500 5.9L Cummings. I went to start it and it acted like the batteries were dead so i rolled it off and it fired right up. that afternoon i got in it to goto lunch (from work) and it started right up, got ready to go back to work and had to roll it off again. when i left work it started right up. Alternatot is charging like it is supposed to. If you let it roll enough for it to jar everything but not start you can turn the key and it will start . I thought that it might be the starter but i replaced the started and the batteries with no luck. Any sggestions? Thanks in advance for any help and soory for the ling post.