I love my Burb, but for some reason it gets unhappy at highway speeds.

At around-town speed it runs fine, but if I take it up near 70 it will chug and miss, especially under load, e.g. climbing a hill. Once the chugging starts it pretty much won't stop. Have to slow down to under 50 to climb the hill which is not ideal for highway travel.

Any ideas? Compression is within spec, but plugs do get fouled in a "we are burning oil" sort of fashion.

Do a leakdown test?