recently my 05..2500 gmc started blowing white smoke, while sitting at red lights, it simultainously runs a little ruff, it dosent do this if cold, if i put it into neutral it stops running ruff and stops blowing white smoke...i have around 95000 miles on it, have also changed the oil, water separator. any ideas??? thanks
RT

 

injectors....have somebody run a balance rate test on them