Cheers for the tip

I took the Focus on a 20 miles trip today to see how it went, and to be honest, it actually feels like a different car. The power (lol) is smooth and right through the rev range, and I no longer have any flat spots, nothing around 2000-3000 or around 5000rpm, it's made a hug difference, and makes me wonder if one of the plugs was actually slightly problematic for some time ?

I actually even over took a few vans without having to drop a gear, I just rolled on the throttle and went, really bizarre.