I have a 2002 2500HD 6.6 Turbo. 268,000 miles. Well maintained. Injectors replaced at 85,000 under warranty. Pump changed 2 years ago. I have now gone from a bit over 15mpg to 13.47mpg. Idle is a bit rough and white smoke from exhause when idling. Could it be anything other than injectors and is there a way to determine which injector might be bad? Thanks for any help and I wish everyone a blessed Thanksgiving!