Car surges when leveled off at high speed.

Yes, I have one!.., Check: Intake manifold and Intake manifold Hoses for vacuum/leaks. Throttle Body dirty or malfunctioning Throttle position sensor. defective fuel pump, Fuel Pressure regulator. Thanks.

Had a car brought in to me doing the same thing, found it was the plugs, someone had put the right type but wrong gap. As they were new plugs I reset the gap correctly and Bingo no more surge.

Of all the suggestions on what it could be, which would definitely generate a code causing my check engine light to come on? Because I should be able to rule those out, right?

That's the problem, they may or may not turn on the check engine light, some will just hold the code in the pending category and not turn on the light until the computer sees it fail again within a certain amount of time. This is why live data scanning is so important as you can see in real time what the sensors are saying to the computer and the computers response to those readings. Then the Tech can compare those to what they should be reading and make a good diagnosis.