Engine misses under power

I have a '95 grand am with the 2.3 DOHC Quad 4 engine. It has been getting poor fuel efficiency for a while and now has a miss(not constant) when under a load(i.e. when the a/c is running and/or accelerating). The service engine light is not on. I have replaced both coils, plugs, wires, coil housing(it was cracked), catalytic converter, and the fuel filter.
I would like to check the fule pressure but can't locate the schrader valve(according to the haynes manual it is present on the fuel pressure regulator, but it's not there).
Anyone have any ideas on poss. problem? Trying to avoid the dealer(don't trust 'em, and they're too pricey).

oh yea, one other thing, when the engine 'misses' there is a "snapping" sound(almost like a high energy elctrical arc) that comes from the upper part of the engine. thought it might be the coil, but the replacement does the samething. maybe a fuel injector?

Any help would be greatly appretiated. Thanks.

Take it from experience, if you replace one-replace 'em all. Cheaper and less headache.

This is what I just had on my 95 Grand AM Quad 4, I had to replace the O2 Sensor. Everything fine now. It did exactly what your saying, Put it in neutral, hit the gas, it should make the same noise and engine motions.

I've replaced the O2 sensor twice. This is what I originally thought to be bad; after replacing, the problem became worse, so I took the part back to Advaned auto and picked up another one. The problem still continues. I've ordered a computer scanner(autoxray6000) and am waiting to receive it before pouring any more money into parts that may/may not need to be replaced. If it doesn't work I'll be forced to accept defeat and take the car to a dealer to have the problem diagnosed. I would still like everyones input though. Thanks to all of you who have replied!!