Does anyone think it is the radiator besides me?

History:
I bought a 65 dart in March, when I purchased the car it had a 68 engine in it. The guy I bought it from said the 65 engine ran but overheated so I put the 68 engine in it. I took the 65 engine to be re-built. So I have a re-built engine, with new water pump a new thermostat and all new hoses. I thought it was running a little hot around town so I had the radiator cleaned up and tested. I also discovered I had put wrong temperature thermostat in the car. I changed the 195 to the correct 180 and all was fine so I thought. Drove out to Carlisle for Chrysler in Carlisle and the car in the am ran a little warm but on the way home it was almost pegged when I slowed down the needle came down a little. Drove it home 3.5 hours slowing down when needle was almost pegged. Didn't lose any coolant. Do I need a new raditr?
Bill

Did you notice any pinging when it was running "hot", the reason I ask is that when an engine is really hot it will ping easily. If there was no pinging then check grounding for your temp sending system and all other wiring related to the gauge. A crusty contact can change the ohms and subsequent temp reading.