Strange Coolant Loss/Compression/Leakdown Situation

Greetings Folks,
Long time lurker and new member. This a great site with a lot of useful information. Thanks for having me. I bought a 2002 T4R 2wd - 5vz a few months ago and it is losing coolant - about a quart per 100 miles. Truck runs GREAT, is just losing coolant. Cooling system pressure test holds 15lbs for 45 mins - no drop. New radiator, water pump, thermostat, timing belt, hoses, belts, plugs, valve cover gaskets, oil cooler hoses and several suspension parts. There is NO sign of any external coolant leaks running or not. Have left idling in the garage (with door open and exhaust blowing out) for long periods of time to see if I could find any external leaks. Nope. Cold compression shows - #1 - 210, #3 - 205, #5 - 170, #2 - 210, #4 - 205, #6 - 210. After a little oil was added to cyl#5, came up to 185. Slight ring blowby. Leak-down test on cylinders 1 - 4 and 6 had less than 5% loss, except cyl#5. Cylinder #5 was losing the large majority of it's air - 80%. Now, where the air is going is what has me stumped.. There is an extremely small amount coming from intake - Barely noticeable without an ear to the throttle body. That's an intake valve. The rest of the air is coming from cylinders #1 and #2. Probably equal amount from each. I rechecked cyl#5 multiple times to make sure I was on the compression stroke and at TDC. Kept getting same leakdown % every time at TDC on compression stroke. Any ideas?

 

You did the pressure test both cold and warm?

 

Only cold.

 

Since it is very inexpensive, I would do the dye test in the radiator that reacts to exhaust gases in the coolant. Cylinder #5 is talking to you.

 

Try do it when warm just in case.

Does that Gen 4R have the trans cooler in the radiator too? I'd check fluids.

 

Forgot to mention that. Already did. No sign of exhaust gases in coolant. Stayed blue after several minutes.

 

All fluids have been changed and flushed recently. All are where they should be and are staying there. Other than the coolant leaking down. Brand new Denso radiator does have trans cooler inside. I also added an external transcooler in series with the radiator. All good, no leaks.

No oil in coolant. No coolant in oil.