ive kinda got the same problem and have had it for a while, on my 03 GT when my A/C kicks in it feels like ive lost half my power, RPMs at idle drop until the car almost dies out, and the battery gauge only take a slight drop...ive replaced the battery and the alternator has been tested and has passed 2 times. when i had the alternator tested though i showed a 2 volt drain at all times that should not be there...all connections are good and i can't figure it out....
2003 Maroon Mustang GT 5 Spd.
18" Bullit Wheels, K&N CAI, BBK Short Throw W/Trick Stick, Centerforce Stage 1 Street Clutch, Pro-Sound Catback Exhaust (Dumped)
2005 Kawasaki Ninja 636 (scary Fast)
Pearl Magma Red, Hotbodies Undertail Exhaust, Powercommander, Custom Tuning, Sunsprocket Front and Rear Sprockets, Interested in Selling