I went though a somewhat similar debacle, 8 or 9 years ago. I was certain in my mind that I had a blown head gasket, as many symptoms pointed to that. But I learned, yet once again, that things very often are not what they seem.

I never did a compression or leakdown test, but after checking for exhaust gas in my coolant, and finding none, I tried swapping 2 injectors, and the error code followed it to the other cylinder. I am extremely glad I did that, because I would have been far beyond pissed if I had either replaced the HG myself, or paid someone about $2,500 to do it, and the problem would have still persisted.

I bought a whole set of rebuilt injectors from a vendor recommended on here (I forgot their name, but possible Motorwest). It turned out that one was faulty, but they quickly made it right, and that particular problem was fixed.