Glitter, you're not going to know without troubleshooting, whether you do it yourself or take it to the dealer. It could be a few different things and without someone getting their hands on that engine there's no way to determine it. It could be a bad coil or spark plug, it could be the head issue. Even if it is a head issue it is not the same as the 2006 issue.
If you wanted to get your own hands dirty you could try swapping coils #4 and #5. You could also put in new plugs. Make sure everything's seated well and that water isn't getting into areas it shouldn't. If I recall correctly, #5 is at the back of the engine and all of the coils sit in a basin. Water will collect at the lowest point, which is at the rear. If the coil isn't properly seated that could be an issue. Perhaps the coil has a frayed wire.
Shell gas as a brand isn't "cheap" gas - each grade has detergents and is much better for your truck than grocery store, Costco, off brand gas stations. I highly doubt it is fuel related.
Sometimes an engine that is moderately rough can be addressed through engine cleaner - Chevron's Techron is considered by many to be the best. But I don't think this is a fuel related issue.
The Internet (and here) can point you in the direction of a few different diagnoses but we won't be able to tell you exactly what it is. You'll have to have someone look at it.
