Keep an eye on your coolant level...if there is the slightest drop then gear up for a cylinder head removal. I've learned that the symptoms you describe have been a blown headgasket (2 occasions) and a bad head on another.

That stumble is one of the cylinders not firing, the stumble goes away and the engine resumes normal operation when the cylinder dries out.

Hows this happen when cold and not warm? Slow coolant leak, as the engine cools down the seepage is occuring...residual leakage is at first evaporated till the cylinder cools down enough...leak still occuring. As casting cools, crack seals and stops seeping coolant. You now have a wet cylinder. Wont happen on a warm engine because there isnt enough time for coolant to collect before refiring.

~Darin <img src="/forums/images/graemlins/baby.gif" alt="" />