1991 Buick Century • 94,500 miles

The initial problem began 300 miles ago as the vehicle would begin to miss on inclines @45mph and not downshift out of overdrive into 3rd gear. Upon hesitation, accelerating hard would cause the downshift and no miss or hesitation. A few hundred miles later to the present day, the vehicle will stall out and sometimes not restart at all.
This is a 3.3L eng. (No codes in the ECM) Loses injector pulse @ half throttle. Will restart cold. At operating temp. Upon acceleration, stalls and loses pulse to the injectors (checked with noid light).
I have replaced: Ignition Module, Crank sensor, ECM, Throttle position switch, Temp. Sensor, oil pressure switch, oxygen sensor. Also had Tune up and new wires, oil and filter change before problem began @ 93,000.
I have consistant fuel pressure of 55 lb and new exhaust front to rear. I have inspected, removed and cleaned all body and engine grounds.
I am at a loss and could use some help. Thank you, Bruce
October 22, 2012.

Just a thought, check for faulty injector. If one fails, the pcm may shut them all down. One or more could fail when they get hot.

Oct 22, 2012.