Recently I changed all my wires and coils with some cheap replacement parts. Car was running fine until it decides that it is going to power down slowly at 75mph. The throttle was unresponsive, but I could cut the car off while rolling and cut it back on again so electrical seems to be ok. I am getting misfire codes only, sometime 1-2-3 some time 3-4-6 and so there is no rhyme or reason for the misfires and so I am wondering if it is fueling.

I changed out my fuel pump, back to my original pump because the new cheap one was quite loud and when the car dies, I don't think I can hear the fuel pump click on when i try to start the car after it's been running.

So, car dies after about 40 miles. If I let it sit for a couple of hours, it will go about 40 more and then cut off.

Car will actively misfire in 3 rd gear at 3500 rpms or higher resulting in check engine light and sometime flashing check engine light. If I keep the car under 3500 rpms, there is no misfire, no check engine lights, no codes, but the car still will die after about 40 miles of driving.

What could it be?