Ok. If it was a "deeper" test, then more than likely, this is a "cylinder compression" test. It's the over-all ability for the cylinder to keep and hold compression during the combustion stage. When it's low, this is more commonly associated with a valve problem or a cylinder head gasket leak. The head gasket leak would definitely show some noticeable symptoms though. And for valves to be bad at 116k is not very common. It's hard to say, without seeing "what" tests they have ran, and the results of those tests. In my opinion however, I find it hard that at 116k, there's a loss of compression and no major symptoms besides a slight misfire.
With that said... it might be a good idea to get a second opinion. I'd recommend a non-Dealer associated shop. There are some very good local shops that have very talented and capable Mechanics. Just to see if they come up with a different diagnosis. At 116k, there are a few things that can cause a misfire- spark plugs, ignition coils, fuel injectors... etc.
As for the price of a new engine- it sells for around $2900 and the Labor Time Guide calls for 10.5 hours to complete the job. Labor rates vary from shop to shop, so what you pay for labor will effect the bot***** *****ne. For a job of this type, a "fair" labor rate can be anywhere from $85-$125 per hour. So $5300 is still on the high side, even IF a new engine is needed. But again... very rarely do you see a 2008 GM v6 with such major engine issues at 116k. I'd strongly recommend a second opinion.
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