[davepl]

Definitely going to be an ignition problem. Here are the basics:

At idle, barely any air is being allowed in. That is squeezed down by the compression stroke, and those molecules float around in your plug gap. But there are few of them, so it's easy to fire the spark across that gap.

Now go to WOT, and not only is the cylinder filled, but the compression stroke compressed them down by a factor of 10. The plug gap is STUFFED with air molecules and it's hard to jump the gap, so the spark will take alternate paths it would not have at idle.

Basically, the more power you're making, the more air in the cylinder, the harder it is to fire the spark, and the more willing that spark will be to find anywhere else to go. That's why someone above suggested shortening the plug gap, which can help if it's really a marginal case.

Bad plug boots are a good place to start. If you have anywhere the headers/exhaust get close to a plug, suspect that as well.