Misfire on 1999 GMC Yukon

Had a check engine light come on this weekend both times were when I was accelerating up a steep mountain pass. The light would come on and then flash throughout acceleration. Eventually just staying on. The code said it was a Cylinder #4 misfire. Don't remember the code number though. This is the first time this has coded this code. Just recently replaced an o2 sensor that was coding Bank #2 Sensor #2. Any relation? And should I start with the plug or is this something bigger?

2 answers
plugs and coil boots or wires should do it code would be p0304 cyl.4 mis detected
no. 3 cylindar misfire with new plugs and wires.