Could be a solenoid. Our Jeep used to do something like that (similar trans). I took ours to the dealer, just bc the right way to diagnose a tranny is to scan for codes, then check solenoids (via a proper scan tool) and ultimately do pressure checks. You gotta do all that before condemning the torque converter. The dealer tool, (or a good snap on scanner) can actuate the tranny solenoids to ensure they are working properly.
In the case of our jeep years ago, it wasn't that expensive and they resolved it in one visit. I gotta give the local dealer 5 stars for that one.
If the fluid needs to be changed, that might be the time to have them do it ....if they need to remove the pan anyway. Maybe you can negotiate a slightly cheaper tranny fluid change. Put in new filters (there are two) also. There are some jobs a dealer should be better at performing with their dealer 'tools' ..and this might be one of them. If they come back with some obscene story, you can always take it to an independent tranny shop for a 2nd look.
Nice looking tk btw! Rams look great in silver.