Mitsubishi Repair: Power loss, watt amp, excessive fuel

Question
Hi, I have a 1994 3000gt base model with the 3.0 dohc v6 engine and 5 speed trans and i have noticed some problems. When i first got my car it had 226000 miles (i know its alot), but it ran great. The starter was bad and was a pain in the ass so i replaced it and everything at that point was working awesomely. The car started quick and consistently every time. Now, having 238000 miles, i have noticed a couple of things. My car starts pretty slow, often times i think it is going to die out. Also there are dead spots when accelerating, for example when i press the pedal probably 1/2-3/4 throttle, i dont feel any power for like a whole second or 2 and then when i do feel the car start to pull it kind of jumps between power and no power up until about 3000 rpms or so. I have replaced the fuel pump (and strainer), the fuel filter, have cleaned the throttle body, and have checked my spark plugs (they were fine). I am pretty sure that my battery is fine because i run a 1200 watt amp and two 600 watt subs without the car on and i can still start it afterwards. Could my problem be the alternator? My dad seems to think that i need new coil packs but at 89 dollars x 3 id rather know for sure if i need them or not. Any ideas? Could it possibly be the maf sensor or maybe i just need a tune-up?

p.s. - the car also has like a raspy tone to it and backfires when revving past like 3500 rpms (at a stand still). it never used to backfire

Answer
True,
You can do a basic check your alternator pretty quickly if you have a voltmeter.  With the car running at normal operating temp, the voltage across the battery terminals should be around 13.5-15 volts.  If it's consistently less than that, than you're probably due for a new alternator.  Running external amps and subs will put an extra strain on your charging system, and can pull power away from other critical electrical systems.  

Engine backfiring can be a result of excessive fuel or late ignition timing.  These can be caused by a number of things, including congested or leak air intake components or even a clogged catalytic converter.  Late ignition timing can happen as a result of poor signals from the crank angle sensor.  Or even a faulty computer.  Read this article for further information:
http://www.90gsx.com/eclipse/cap/caps.htm

If your ECU is faulty, it can contribute to may of these problems.  It's worth checking it out if the problem persists.  
Good luck!