I'm sure you probably have but did you inspect the weep hole on the water pump? I kept losing coolant at about the rate your describing and for the longest time I couldn't figure out why. Then one day I was doing something in the engine bay and noticed what looked like a very small wet spot under the weep hole. Changed out the water pump and no more coolant loss.

 

Thanks for posting the update. I'm so appreciative when people do that I always like to post and send a thanks!

As for the leak, I heard of someone having a pin hole leak that only let water out when the system was hot/pressurized and that it leaked onto a hot surface that caused the water to evaporate. Have you tried pressurizing the system to look for a leak? I guess this would also apply to a leaking LIM gasket.

 

I had a crack in a plastic tank that only showed up when the truck was running and very hot. Should have found it when you pressurized the system so I would look at the cap and/or the water pump.

 

when tightening the LIM bolts there is a very specific procedure on these engines. Including a final extra turn on one of the front bolts on the drivers side. I think it is the second one back. In all my years wrenching I never would have known if my brother hadn't given me the repair manual from when he owned one. Hope this helps.

 

I also forgot to mention that a LIM gasket can leak internally to an intake port and the coolant would probably not make it into the oil. It would just blow right out the exhaust.