12 will always be there. No good reason for it, it just is. 55 is end of codes so you have no codes.
One other thing that I haven't run into on a Mopar but I have on many GM's. If the lockup convertor isn't releasing it will kill it at stop lights. If you slowly come to a stop does it seem like the engine is draggin it down like a manual in gear and braking to a stop?
I doubt that is it and I am still hedging my bet on a vacuum leak or intake pan leak (also a vacuum leak).
