keep an eye on your alternator pulley. if its locking up and causing the belt to squeal against it, that could be why your battery light comes on. if your alternator isnt spinning, then it wont produce enough voltage, and if the voltage is below 13v or so then the battery light will come on because the battery is not being charged. it may be something else causing your engine to slow down though. cant say with this little info.
2002 GT 5sp. 16x,xxx miles
Steeda Exhaust, C&L plenum, BBK Throttle Body, Steeda Underdrive, Steeda short throw, unknown stage clutch. Rear main leak. Compressor seal leak. Steeda lower control arms. good tires.