where is the location of a pcm on a 2004 buick lesabre? stalling and power loss issue..

I have changed just about every part on the car that has to do with sensors as well as
control modules..(TPS, MAP, MAF, ECM, plugs, wires, coil packs) this is the last
one.. i am having mixed results on where the PCM is located..  Car has random loss
of power and even begins to "deisel" in sound with a total loss of power until the car is
shut off and restarted after a few minutes, the car begins to run again. With limited
power and it also has begun to have a tick in the motor that was not there before.. The
only error code i keep receiving is for a faulty TPS  this part I have Replaced two
times as well as the catalytic converter was the last item put on the car..  As you can
imagine it has become quite expensive since no one can seem to say what it is..
Midas told me it is the PCM.. once again same symptom yet different answer from a
different shop.. I have the new pcm and have already had the item Flashed to the vin
number on my car it is ready for install.