My 'o6 250 has about 65k miles on it..and when I really nail the throttle I see "smoke" from the exhaust. Not heavy black or blue or white. I see it more after dark looking in right mirror with headlights back lighting this. It goes away at say 85% throttle, and is worse towing a small tandem trailer..maybe 6000 lbs gross. No chips or tunes..all stock engine. It is about time to change fuel filters again..gettin close to 35 k on this set, most I've ever went betqween fuel filter changes. I remember seeing this with lots of older diesel engines and hate to think of it happening to mine.Any ideas as to what this is? By the way its 2000 miles into an oil change, with same on new air filter.