There is a test system that allows you to check all traces of coolant in the combustion chamber. You should try that, but I'm sure others here will give you more information.
Here's my personal help;
Let's take what we know, and go from there. You say that the upgraded gasket and bolts would more than likely block any traces of coolant from getting combusted. So, from my past coolant loss experiences, it's more than likely a leak. Where? I don't know, but there are only so many places it could be going. Start off by doing these steps
1. Chemical test for coolant in combustion chambers
2. Remove the overflow, run water in it and let it sit inside your house for a few hours. If it leaks, there's the problems.
3. Check the hoses like this, take a white paper towel, and run it down across the coolant lines that are visible. If you have green (Or the red pre-mix) color on the paper towel, remove and examine the line, replace if necessary.
4. Check the spark plug galley for coolant, that's a common place. If you have coolant there, check for lines leaking around the galley.
5. Start the engine and let it idle until it gets warm (Normal temperature), see if you can smell coolant burning. If so, look around the exhaust and block area. (This narrows down your problem)
And also, if you have drained the coolant and refilled, it will be taking the fluid from the overflow into the coolant system.
Just trying to help you out a little,
Matt
