2001 Ford Ranger Power Loss

I have a 2001 Ford Ranger with the 3.0 Flex Fuel V6 mated to a 5 speed automatic. Currently she has 285K on the clock. Most everything under the hood is original, save for the water pump, fan clutch, radiator, upper & lower hoses, thermostat and timing chain.

I am having an issue with coolant loss. It’s not leaking externally, that I can see or smell, but it is leaking quite a bit. As of this morning, it’s up to a gallon every other day, roughly.

She runs very well, aside from a little power loss at high rpm; it feels like a fuel loss issue. She’ll stumble above 4.5K and then pick up if I back out of the throttle. Usually this is accompanied with a flashing, but sometimes steady, check engine light. The code is for a misfire on cylinder 4.

My question is this: with the coolant and power loss, how possible is it that a head gasket has blown and it’s burning coolant in cylinder 4?

When removing the spark plugs, none are white and all look about as you’d expect for the mileage on them (45K as this time). There is no coolant in the oil, and the coolant pressure test holds steady at 16lbs. I left it on pressure for about 20 minutes and it didn’t drop.

The truck runs very well aside from this, it has no rough idle, good power up to the above mentioned 4.5K, and still gets the 21mpg it’s rated for on the highway. I had no lack of confidence in taking her cross country, prior to this.

I will be doing the exhaust gasses in the coolant test tomorrow, in case it passes that test, does anyone have some experience with something like this and could point me in a good direction?

I appreciate the assistance and apologize for the wall of text.