Just an experience to share here, might be useful for others with same problem.
I started noticing a coolant loss but no obvious signs of a leak. Just having the engine rebuilt I was fearing all kinds of internal leaks. Put the whole coolant system under pressure at around 18 PSI through radiator cap opening and it held the pressure for 2 mins or so while still no signs of leakage. My first suspect became the radiator cap given it's age, I changed it with a new one from Auto zone for around $6.
Things got better but still noticed a tiny bit of coolant loss (in reservoir tank), while just looking around the engine bay I noticed some black caked residue around the coolant hose attachment to the throttle body. I opened the hose cleaned up the area and cut about an inch of the coolant hose and re attached it. So far the fluid level is steady in the reservoir.
As a side note, I did not experience engine over heat during this coolant loss. I noticed this during her first offroad experience to the Argentine Pass <img src="/forums/images/graemlins/smile.gif" alt="" />

your rebuild did not include new hoses ????? watch all your clamps

look under your floor mat in the front could be the heater hose or core?

I blew one of those Trottle Body hoses on a 105o 4th of July.
It cost me big .
.
Replace those hoses ASAP with high quality hose.

They are no fun to replace down there between the firewall and engine when it's hot out and your engine is red hot with 2 newly blown headgaskets cause you didn't replace them on rebuild.