To determine if your truck is an early or late 1999 model year, locate the tag on the drivers side door. Vehicles built before 12/7/98 are considered early 99 and vehicle built after 12/7/98 are considered late 99. What does this mean? One difference between 1st and second generation is early(1st generation) 7.3 power strokes have a mechanical lift pump located in the vally of the engine. Horse Power and Torque increase for 2nd generation and servel other differences see chart below  for horse power and torque specs