Truck isn't starting, studders when trying to turn on and just isn't catching. Service light isn't on so the auto shop couldn't test it to find the problem, any ideas?

 

It is unfortunate that some repair places can't do much of anything without depending entirely on the check engine lite. There are the basics that should never be overlooked among which are fuel and fuel quality, air, compression, timing, battery condition, blocked exhaust etc.
After these are confirmed functioning properly, then we go to more specific subjects.
It might be time to try another shop.