2001 4.7L 4WD QC. I had been getting some extra air in the coolant system slowly over time, enough to push the coolant into the reservoir and start overflowing. Been hunting for air leaks that could be drawing air back in but nothing, so I ran a combustible gas test and it came back positive that the trapped air in the coolant system is definitely exhaust gases.

So my next step is to try and pinpoint, as best I can, the head in question and even better, if I can, which cylinders are affected. I ordered an OTC leak down tester yesterday from Amazon so we will give it a shot this week. I am pretty much planning on having to pull the heads, just figured I would do a little more diagnostic testing before I lost the opportunity. Guessing cracked head or leaking head gasket.

Anyone have this issue before?

 

You hit the nail on the head, leak down tester. Going to help you pinpoint it to which head, but you won't know if it's just the gasket or if it's the head/block until you've pulled it.

Haven't done much work on the 4.7s, but I know they're a bugger when pulling the heads keeping the timing in line, good thing there's a link to a free factory service manual, which just so happens to have a good segment in it on doing headgaskets in 4.7s!