Here is a diagram which shows the various solenoids (PCS, TCC-PWM and Shift) located in a 4T65E transmission. These are located under the side cover assembly (left hand side). Also, applicable to GTPs with the 4T65E-HD.
Refer to the SPID label located on the back of the trunk lid for which autotransaxle your Grand Prix has. RPO codes are as follows:
M15 - 4T65E
MN7 - 4T65E-HD
Note : Some Grand Prixs '97-'98 may have the M13 4T60E. However, all L67 GTPs from '97-'03 were delivered with the MN7 4T65E-HD.
EPC = Pressure Control Solenoid (PCS).