Fuse #6 and #39 is a common source for the power drain on these cars.
When operating normally, remove fuse F6. Put your meter in place of that fuse and set on Milliamps DC. When you close the doors with the car off the meter will read over 200mA (I have an LED dome lamp - yours may vary) until the dome light shuts off. Then the meter will read about 112mA for about 40 minutes. After that the PCM goes into standby and the meter will read about 12mA steady state.
Anything else, and you have something causing a parasitic draw on the battery. Most common source tends to be the Mach 460 amps. They are supposed to go into standby mode but as they age the internal compoents fail and should be replaced (caps). Try unplugging the amps and see if that solves it.
Some reference wiring diagrams here
Fuse #6 also feeds
1 20 amp--------Lighter
7 15 amp--------Main light switch, Generic Electronic module
13 15 amp--------Electronic flasher
19 15 amp--------Park lamp relay,Exterior rear view mirror switch, Master window/door lock control switch, Right window/door lock
25 25 amp--------Luggage compartment light
31 10 amp--------Data Link
I'm going through a similar drain on an '00GT but haven't gotten that far in testing yet. Mach amps are so common that's going to be the first thing I unplug.