Itteh, take the bloody filter off, there useless on anycar let alone an 8v! get a standard air box for the thing, unplug all your connectors, give them all a dam good clean, have you tried getting a new battery?? Jus because it might be reading 12v and your alt is putting out 13v doesn't mean it's all good. The battery could have a dropped a cell over winter and then when under load may just be giving out, I'm betting you have a nice big sub in there too that will be kicking the ass out of the battery that your little 8v alt can't keep up with. Your doing the worst possible thing which is diagnosing through replacement, and it's the wrong way to do things, you could have ruled out your dizzy, rotor arm and lead simply by checking for a strong consistent spark at the end of the leads, or better yet you could have unplugged them one by one and stuck another spark plug in them and checked for a consistent spark thus ruling out everything you've replaced, my father in laws car kept cutting out mid driving no matter how far or short of a journey he went, no matter what speed he was doing, wouldn't even turn over sometime even after driving 20-30 miles, new battery and it hasn't done it in over 2 months now.