I just bought the truck did a test drive everything was good. Got it on the rode and the fuel clamps came off and leaked fuel. Got them clamped and noticed white - gray smoke and noticed loss of power. What could it be?

White smoke is a sign of water vapor or fuel that has been atomized, but not burned. Water vapor may be present in the fuel, or water may be leaking into the cylinders from the cooling system. Also, air in the fuel can cause white smoke. White smoke usually occurs when there is not enough heat to burn the fuel. The unburned fuel particles go out the tailpipe and typically produce a rich fuel smell. It's not unusual to see white smoke in the exhaust, during cold weather, until the engine warms up. Bad glow plugs (burned out, coated with carbon, or not receiving proper start-up voltage) or a faulty glow plug control module can cause white smoke on engine start up. Low engine cranking speed may also produce white smoke. If white smoke is visible after the engine has warmed up, the engine may have one or more bad injectors, retarded injection timing, or worn injection pump. Low compression can also be a source of white smoke.

Was this the Powerstrok Turbodiesel? Definitely have the cooling system checked for hydrocarbons... that engine I have heard from many people is prone to cavitation damage if the nitrate levels in the cooling system are not maintained well over its life. What happens is pinholes develope in the cyclinders into the waterjackets... when it gets bad enough you hydrolock the engine and destroy it...

Remedy is having the offending bores sleeved... not a simple or cheap process.