I have a 97 Dodge 4x4 automatic with the Cummings engine. I've had the same problem, but to add more to that I've gone through 7 transmissions. A buddy thought that it might be the tranny causing the raise in temp because the tranny fluid runs through a seprate core in the same radiator. I've changed out the thermostat to a lower temp one, replaced the water pump, installed twin electric fans, and installed the biggest trans cooler for the tranny alone and it seems to work for the enigne. The tranny has been my biggest problem though. Also check your water pump. It might be starting to go. I hope this helps a bit.