How to tell if car is NPI or PI GT???

Anything 99-04 is PI.

What they were probaly talking about is the intake manifold. 99-mid 01 had the same crappy plastic coolant crossover as the non-pi 96-98 GT's did, but it was still a PI manifold.

If thats what you are reffering to then just pop the hood and look at the thermostat housing. If its sitting on aluminum and not plastic you are good to go. If its still the plastic one then its going to crack sooner or later.
 
so my 2001 gt is def. a PI motor? and if i have the plastic crossover piece should i even worry about getting the aluminum crossover???

at some point the plastic one will start to leak.. but I am 10000000 percent sure your car is PI

Many people get confused by the fact that ford made PI plastic crossover intakes 99-mid01 my old 2001 had the plastic one and I changed it.