So I picked up a 2008 ram 2500 with a 6.7. I'm working on swapping in a 12 valve and need to know what the pcm on the firewall controls? Does it only control the trans or is it all the gauges and a/c? I know there is a ecm on the 6.7 engine itself but I can't figure out if I need the ecm to get the truck to run properly. Any info would be a huge help thanks