93 Geo Prizm M/T 1.8 ignition code

I have some sort of electricial problem, I'm getting a ignition problem code. I've replaced the whole distributor, wires, plugs, O2 sensor, throttle position sensor and sent out the computer and had it checked. Even took a computer for a runner and had the same problem. The car starts fine, takes off under load and doesn't miss a beat but get to a constant speed and she starts to miss. But the longer you go at that constant speed she'll tend to smooth out. So let's say you have to stop and start again, it will start all over again. Now every now and then after she's warmed up she'll start up and stall and maybe run rough, no rhyme or reason. Anyone have this type of problem, any ideas out there. :banghead: