ChevySuburban00

I have a 2000 chevy suburban 5.7. I am losing coolant not leaking anywhere visable, notice milky oil but not there anymore, and loss of oil pressure according to my guage but no change in the way the truck ran or idled. i run synthetic oil high milage just changed 300 miles ago and all oil leaks repaired. I am at a point to where i am just stumped. i cant find the coolant loss and not sure why i would lose oil pressure at the same time i lost coolant. Truck did overheat on highway filled it up got home about 10 miles away and again coolant almost gone. Any thoughts? Thanks, Chevysuburban00