i have a 2005 dodge ram 1500, i bought it used and had no issues and after a few weeks once winter here in Canada rolled around in the colder weather or when the engine was not at operating temp it seemed to drop rpm and sometimes stall when i shift from park to reverse or drive, also when i come to a stop at a light or stop sign. i cleaned throttle body and air filter which seemed to help but not fix it so i cleaned the egr and pcv valve helped again but did not fix. the other thing i wanted to do is the iac valve but it is built into the throttle body so i just left it. then i changed transmission fluid and both filters and filled it with ATF+4 ONLY! and seemed to get better as i added fluid. once i got the exact amount of fluid in it fixed the problem 100% have not had any issues since. thought this might help since it seems to be a common issue with rams

 

Your right, the transmission needs to be fill to the line. Even a quart and a half low, it will stall when cold.