Are there electric fans? Be sure those are coming on when they should.
Also the temperature sender for the gauge in the vehicle and/or coolant temperature sensor for the engine computer can be giving false readings. Although when I have had those go bad in the past, they indicated too cool. But might want to test those as well.
Complete testing and troubleshooting instructions would be in a 99 Dodge Caravan factory service manual set of books. Order from dealer or online at alldatadiy.com