can anyone help me understand why the 2007 ram hemi im working on keeps cracking the #5 coil as soon as you start the engine ?

 

How many has it cracked? What brand are you using?

 

Post up a pic. This sounds weird.

 

The PCM is grounding the coil and not letting go. It steps up several times until it can't handle the stress and almost explodes and cracks like a boiled egg. Make sure the coil control circuit is not grounded to chassis ground before you replace the PCM.
DO this by unplugging the PCM and the coil then check for continuity to ground.

I see this a handful of times per year on the HEMI. Usually on ones that have neglected spark plugs. Over time this wears on the PCM internally.