So lately I've been losing coolant rather quickly, took it into a shop where it sat 4 days on 20PSI and they couldn't find where it's going either. I've changed the reservoir cap as well thinking the seal went bad. I don't believe it's a head gasket either as the oil is not milky, and there is no visible leaks/drips anywhere. Could it be a manifold gasket? This is keeping me up and night and stressing me out! I'm DESPERATE guys! PLEASE HELP

 

If it's a manifold gasket it will show up on the dip stick

 

Try some Barr's block seal. It is a temporary fix that might work for you. I had that problem on my old Silverado and coolant was getting into the combustion chamber and burning away. There were no visible leaks.