My 2003 2500ec 17,000 mi. has started smoking at idle (light greyish) and seems to be idleing slightly rougher than it used to. I have a freind with a Tech II he said the injectors were all doing what they were supposed to and there were no codes. I'm supposed to be going on a trip about 2K round trip on sat. I know DSL's typically smoke but mine never has. is this normal?? Oh and the low boost fuel in on level 1 on my attitude.