2007 Hummer H3 Mis Fire

Is your check engine light on also? There is an issue with the cylinder head on the inline 5 cylinder where it misfires at idle, and goes away above idle. Most often, I have seen #5 the one with the most misfires. The machining on the cylinder head was the issue, and is solved by head replacement. You don't have mileage listed, so I don't know if it is under warranty still, or not. This was most common on 2006, but I have done two on 07's in the past three weeks. This is not the only possibility, just highly probable, with your symptom. It can be confirmed with a cylinder leakdown test. If it is out of warranty, there are special tools and procedures required to do the job, and not have to remove the front cover to reset the timing chain tensioner.