Truck runs rough after servicing

What plugs did you use? And are you 100% sure that you got the plug wires routed correctly? And last but not least, which engine is it? Is it the 4.3L, which is a V6, or is it a 5.7L, which is a V8? Both are available in this truck.

Actually I stand corrected. There is a 4.3L V-6, a 4.8L V8, a 5.3L V8, and a 6.0L V8. The first image below applies to the 4.3L V6. The second applies to all V8 models.

I hate to say this, but of course they are going to say it has nothing to do with their work. They do not want to spend the time (unpaid) to fix it. I suggest you check the work yourself using the diagram that I posted above. I also suggest making sure that each wire is fully snapped into position on both ends. A loose wire or two will cause misfiring, and no amount of poking around with the engine running in the middle of the day is going to catch it.

You really should check that yourself. If that does not solve it, then you should check the spark strength yourself. Here is a guide on doing that: https://www.2carpros.com/articles/how-to-test-an-ignition-system

And here is a link to a spark tester: https://www.amazon.com/Lisle-20610-Inline-Spark-Tester/dp/B0002STSC6/ref=sr_1_3?ie=UTF8&qid=1501325755&sr=8-3&keywords=spark+tester

To me, the idea that they somehow cleaned the fuel injectors and managed to make them worse, not better, is a bit fishy sounding. You can try running a bottle of SeaFoam through the system along with half a tank of premium Shell or BP Fuel. Be sure to open the throttle up several times. Run it hard. If there is something clogging up the injectors, that is about the only way to knock it loose without taking the injectors off and cleaning them again.