can it be anything else besides a blown head gasket?

[billy j]

I have a 2000 mustang gt, about a year ago I replaced a engine due to a blown head gasket, oil was running into the coolant, well I swapped the engine out with another one with 60k miles, ran real good for a year, and I get home and park it everything was fine, then I crank it on the next day and its running real bad kind of like its running on 3 cylinders, miss fires, it idles real low and turns off, I checked the coolant looks good and on level, then checked the oil cap looks like real little water mix and it has 1 or 3 air bubbles on dipstick, all this happened all of a sudden and the day before it was running just fine, I was wondering if this could be anything else besides a blown head gasket as it just happened all of a sudden