1: Stop driving the truck until you find out what is going on
2: Park your truck on a hill, nose down, then remove the egr valve and clean it. CLICK HERE
for directions how to do it. Leave the valve out of the truck overnight. In the morning, check the hole in the intake for the presence of liquid. If you see any, your EGR cooler has failed and your oil cooler is plugged up in the coolant passages. This plugging is what caused the egr cooler to fail. The coolant exits the oil cooler and is directly fed to the egr cooler. The plugged up passages slows the coolant flow to the egr cooler. The slower moving coolant allows the egr cooler to overheat, and it fails internally. The coolant will then leak into your air intake stream every time the egr valve opens. This would explain the white smoke and quite possibly the knocking noise that you heard. The turbo can also be effected. During the time that the coolant is not being sucked into the engine it is flowing out into the exhaust system. This will also result in white smoke. The exhaust flow will force the coolant to flow upwards into the turbo on the exhaust drive side of it (and also where the vanes that control your boost are).
Even when the truck is shut off, the coolant can still flow out of the egr cooler, stack up behind the egr valve and also flow into the exhaust. Since there would be no exhaust flow to force the coolant upwards into the turbo, the coolant would flow down into the exhaust manifold and into whatever cylinder has the exhaust valves open. If enough coolant gets into the cylinder, you could hydrolock the engine.
The end result of all of this carnage? Possible head gasket failure. Should enough coolant get into the combustion chamber, it would raise the cylinder pressure beyond what the stock head bolts can withstand, and the bolts will stretch. The head gaskets would then blow.