I had the same problem with my 01, 94000+ miles on it. It would misfire occasionally only at idle at a stop sign or light. On Monday it went from occasionally to always. Mine was the cylinder one according to the code, bought a plug an coil and changed it in about 30 minutes. My first plug change on this truck and after reading all the horror stories about breaking the plugs I was real careful. I'm going to change all the plugs this summer when the weather is more conducive to working outside.

 

The 01 doesn''t break plugs - they blow out if not torqued properly. It's the 04+ 3v engines that break them.

 

$20 says it's a coil going bad, and once one goes, they all do....

 

I had a 2001 F-150 that did what yours did, and come to find out a vaccuum line collapsed. I never got a code or anything, and it only did it sporradically, though I only drove it 15mi until it was fixed. Hope that helps.

Oh, and I had a misfire last weekend. It flashed the check light at me immediately.