2006 GMC Canyon Won't start sometimes

Just recently the truck has started to not start. I the engine engages but it will not fire. Took it to a shop. The fuel pump, starter, and battery were fine. Now I am starting to think it could be an iginition problem. What do you think and how can I get this checked? Although the engine does try to start it just won't fire.

Problem is to get it to the shop it has to run and if it's running everything checks out just fine. It's a mystery.