99 5.2 Misfire

[sentrek]

My sons truck is misfiring again. About 2-3 weeks ago I swapped out the ignition coil with a new one because the engine light was on and the code was for a Cylinder#6 misfire. It fixed the issue and truck was running great until now, now the engine light is on again and it is for Cylinder #8 misfire. Roughly 115,000 miles.
Any ideas what might be causing this, seems unlikely it would be the ignition coil again?

 

[18CrewDually]

Pull and inspect ignition cap & rotor. Replace if any signs of burn or corrosion growth on any of the terminals. Also inspect wires, replace if old and you're replacing the cap anyways. Pull sparkplugs and replace if they show wear and out of spec gap. That's a typical tune-up.

 

[sentrek]

Cap, rotor, plugs and wires all have roughly 3k miles on them. Bought the truck with 112k miles, first thing we did was a tune up (by a local shop). But I can still do that.