Hope I'm not too late.....first thing I would do is try to determine where the leak is. A vacuum gauge will flutter if the intake valve is hanging, and a 3x5 index card folded against the exhaust outlet will snap back if it's the exhaust valve....this is most of the time, not 100% but a good starting point.
You could have a piece of carbon, part of a ring, something stuck in the valve seat, sometimes it will pop or backfire through the intake if it's the intake. I would pull the valve cover and see if any of the valves are hanging, should be easy to tell.
Please post progress before you think about pulling the head, it's somewhat involved and you don't want to drop the chain, especially since you have a 4WD.
Many people report breaking head bolts and I would think one way to help against this is to warm the block...question is how?
I was thinking about this months ago if I ever had to pull the head and I personally would want to try to release some of the tension on the bolts, one way is to warm the block and I thought of a block heater, or something that could warm the coolant without running the engine. Not sure what is out there but another option is to fill the block with hot water after you drain the coolant.
Right before you are ready to break the head bolts loose, I would fill the block with hot water...maybe 180-200 degrees and that's just a guess. Maybe go with 120-140 deg water to warm it slowly initially, then drain and add some hot water. This should expand the aluminum much quicker than the hard steel bolts. Then, rap on the head bolts with a hammer before you turn them.
I honestly feel this is a better way then going about it with a cold block....it's at least worth a shot and physics is on your side.
Now for the important part.....don't try to mess with the timing chain until you have an understanding of what all those bolts hold together under the cam chain cover...ie. the valve cover in the front. Get yourself an appropriate tool to hold the chain in place, and make sure it's secure. Once it's secure, use a bungee strap with a hook and make a secondary catch just in case it comes loose.
Make no mistake, if you drop the chain, your nightmare has only begun. You will need to pull all 3 cross members, the steering rack, the front suspension needs to be separated to pull the axle shafts from the oil pan, the front diff needs to be removed from the oil pan, then the oil pan, then the front timing chain cover which means everything from the fan to the accessories bolted to the front cover.
At this point you would replace the front cover since it's the oil pump since it's a mountain of labor saved if it ever goes, as well as the rod bearings since the pan is off.
Morale of the story is...... Don't drop the chain.
