I bought a used 2004 Rancher AT with only 120 miles on it. It runs fine except after it is warmed up and working hard (pulling up a long grade in warm weather etc.) the engine seems to loose power and makes more noise. It just feels like the engine is tight. After it cools down it is fine again. The fan runs and the oil cooler fins are clean. Do you think the engine just needs broken in more? I also bought a 2005 Rubicon with 120 miles and it runs fine in the same conditions. Any ideas?