Vehicle: 2013 RAM C/V with 219k

Situation: while in motion the van starts to overheat. When you come to a stop and sit idling for a minute or two, the temperature gauge quickly returns to normal.

It just had come back from the shop after the transmission was replaced. We originally replaced the transmission back in April and the replacement transmission failed; the new one was replaced under warranty. Other than that, the van is behaving normally. No loss of power or anything. So, what could be causing this?