I have a 1995 Dodge dually w/ diesel engine in it. I can crank it & start to drive and it shuts down. I hold the gas to the floor and it smothers down w/ white smoke rolling out the back. I wait a few minutes & crank it again if I hold gas to the floor. It stalls and I can barely get to where I am going. I have to keep holding the fuel down all the way. Can you help me find out what might be wrong?