i don't know what yoear your truck is but the 250 i put in my 64 ran hot in the summer and towing for 2 years. not as hot as yours but it could creap over 200 sitting at a light. when i would pull a long hill the temp would climb, when i would go down the other side with the truck pushing the engine it would cool down. the orig 6 rad tested ok but i switched it out for a new v8 one and that took care of it. no more fluctuations at lights or hills.
