Just another thought, did the original engine prior to this one installed, have a blown head gasket?
If so is this the same exhaust being used? If you answered yes........ the symptoms being explained are consistent with old exhaust filled with old oil and antifreeze coating on the pipes and will eventually burn off. Run it till it till brake in period on the correct RPM...THEN RE TORQUE AND REPEAT BREAK IN..CHECK THE FLUIDS...
