The 4.3, 5.0, and 5.7 engines had the GM intake gasket leak problem in the late 90s/early 2000s. I'm not sure if this was fix by 2005. Any coolant in the oil, even a few drops is a sign of an intake gasket leak. The only sign of an intake gasket leak on my 2000 Blazer (4.3) was a slow loss of coolant (~1 pt/month) and an occasional smell of coolant at the front of the truck.
There was no milky goo at the oil filler cap (sure sign of excessive moisture in the oil) and the oil was clean. A few drops of coolant showed up when the last of the oil was drained out of the pan. That was enough for my mechanic to recommend getting the gasket repaired. The dealer confirmed my mechanic's diagnosis and replaced the gasket. This is not a repair to hold out on, because any amount of coolant in the oil displaces the oil from the main bearings, wrecking the engine in a short time.
A few years ago the Blazer had the same symptoms and it turned out to be a crack at the top of one of the radiator's side tanks. I didn't find the crack until the radiator fan shroud was removed.