I'm new to the Cummins myself for around 3 months now. The auto trannys do not like much more power than stock. They can be upgraded though.

In my opinion, this is the Moparts of the Cummins world...

http://www.cumminsforum.com/forum/

Another good one, just take your pick...

http://www.dieseltruckresource.com/forums/

1972 Cuda 340 4 speed, 2001 Ram CTD 4x4 6 speed, 1970 Duster 408 4 speed, 1996 Ram 5.9 2x4 auto, 1965 Coronet 500