2006 f150 fx4 112,000 miles. Truck started to shutter at 55 mph on freeway and check engine light came on. The shutter went away but the check engine light stayed on. I pulled the codes and it said misfire on cylinder 4 and 8. I had the spark plugs changed at 88,000 with motor craft plugs. Could it be plugs? Or maybe coils?

 

Could be the coil (or just the boots/springs). You can swap coils for those two cylinders, see if the code follows.
Couple of things to check, proper plug torque, COP connections clean.

 

Or even a bad plug from the box.. or cracked plug during install.