It all depends upon the condition of the motor.
If you've a worn out motor, that would be the reason for the problems.
But, if the motor is in good condition, and you verified that the plugs, wires, and coils are good, the next candidate would be the ignition.
When the cylinder pressures increase, like when opening the throttle; and the rpm's are optimum for good pressure, the force needed to fire the spark plug is greatly increased,,,, strictly due to the high pressures.
When the ignition module starts to go bad, it, as the controlling instrument, acting as a grounding device, has a difficult time grounding the current coming from the coil(s) and thereby effectively reducing the potential of the spark and the demand of the coil(s).
And so, if your motor is in good condition, that explains what could be going on, (or off) if you may!