If you can, ALWAYS hear the truck run. Thats gotta be one of the best things you can do. While running, take a long dowel to different parts of the engine, with you ear on the end and you can hear things you couldnt normally hear, slight ticks and knocks.
Also check the oil. I always pull the dipstick, look at the oil level, look at the oil itself looking for reflective bits of metal shavings, rub the oil between your fingers cause you can often feel things gritty your eyes may not see, and smell the oil to make sure its not gassy or burnt smelling.
Jeff
