99 Sunfire - Cylinder misfire - popping sound on Highway

[canadiancynosure]

Have a problem and mechanic can't reproduce the problem so hoping someone here can help.

1999 2.2L Sunfire
I've been able to reproduce - when I drive upwards of 120km/h on the highway I feel a sudden loss of power on the car and it drops to 90-100km/h.
The engine does not respond when I try to accelerate and instead the check engine light starts flashing and the ETS Off light illuminates.
The car the idles very rough when at a stop.

The mechanic says error code was Cylinder 1 misfiring - however the plugs and wires appear to be fine, especially since the car is smooth when driving at
lower speeds on side streets.

At one point I could hear a hollow popping sound from the engine for 30 seconds - one time at a slower speed and another on the highway.

I've recently replaced the wires, plugs, coil pack, air filter, oil change.
Exhaust system is only a year old.

Need the car for a few more months before I buy new. Hoping someone can help me out.