Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
What year and model is your GMC? Engine size?
Does the check engine light ever flash? Do you feel a misfire while driving?
Have the plugs and wires been replaced recently?
You would think that the GM garage would have done all necessary repairs, but obviously they missed something. Misfires under load are caused by faulty ignition system components. Plugs are likely okay, but I suspect that you may have some bad plug wires.
Yes a failing coil can cause the same symptoms.
That is an odd one for sure. Not something that would be expected. We did see a lot of camshaft failures in the 1980's on GM V8 engines, but it is not common today. Glad you were able to get it sorted out, sorry that it is going to be an expensive fix.