The two big issues with that symptom (and we've had people come on here many times saying the same thing) are fluid level and conductor plate issues.

Of course, if the car sits in the rain a lot, and you are not keeping the cowl drain clean, water backs up and flows down the HVAC intake, then onto the floor under the passenger's feet, then into the audio PA and Transmission Control Module - but in such cases, the car seems to simply quit shifting altogether. This one is easy to find you yank the carpet down, get under the shield, and look for water damage/intrusion. If it's wet under there, unplug the electrical connector from the TCM - if it's wet/corroded, you found your problem. Go find a TCM from another automatic Crossfire (TCMs in SRTs are different from Limiteds) and also get the last few feet of the wiring harness, as you cannot clean the pins in the connector.

There are threads here on the conductor plate issue as well as fixing low fluid levels (which are caused by leaks around the electrical connector on the transmission - VERY common).

STOP driving the car until this is fixed or you will be really sorry.

Here is an index of threads and PDFs on common problems:
Click here