Cpde question???

[wwotr]

My Wife & I bought an 05 GMC Sierra Ext Cab about 2 years ago.
At the time, we bought an extended "Bumper to Bumper Warranty".

About 2 weeks ago, it seemes to (ever so slightly) stumble, slight hesitation and the engine at idle seemed just a little rough.

Then about a week ago the "Check Engine" light came on.
We took it to our local mecahanic.
About 3 days later I stopped by to check on things.

The 1st words out of his mouth were, .......
"please tell me you've bought an Extended Warranty on this"?
He says he checked the engine and it was getting Spark and Gas.
He then checked the onboard computer and,
(if I can read his writing correctly), got a Code of #P0300 or P030D.
He says that compression in #2 & #7 were low on Compression and to have the Dealership run a Leak Down Test.
He thinks it's the very begginings of Burnt Valves or Worn Valve Guides.
He was surprised to see that on an engine with only 133K miles on it, exibit this kind of trouble. He's expect that on an engine that had 200K or more on it. So I havent heard back from the Dealership yet, but I thought I'd ask the more knowledgable people here what THEY thought the pronlem may be and how it should be taken care of.
My mechanic said they may just slap a new set of Heads on it,
or that the Sealerships have this "additive" that they can pour into the engine that seals/rebuilds the "Top Side" of the engine.

Thoughts/Comments on the whole situation would be welcomed.