Chevy 1998 p/u 5.7; I have water in my oil

The head gasket is probablly bad. Other possibilities could be cracked head or block. the gasket is the most common.

sound like the engine has overheated and needs to have the heads removed and inspected for gasket failure and sent to machine shop for inspection and repair. you can have the engine tested for hydro carbons in the cooling system if you have the tools. also need to check the cooling system for failure to find the cause of the overheat. suspect leaky water pump, radiator, hose, heater core, stuck thermostat, worn ot fan clutch.

Cracked head

You more than likely have a bad head gasket. Take it to a mechanic and have him do a preasure check on your radiatorif you are losing pressure then it is going through you head

Although I have seen people put oil in their rad by mistake , or windshield washer fluid in their brake fluid res. etc. The most likely reason for water in your oil is a blown head gasket.
If you also have oil drops floating in your rad , that would pretty much confirm it.

Most likely your intake gasket needs replacing. They are very common to fail. Your local auto parts store should have a new re-designed gasket made by fel pro with a metal frame with silicone inserts. To make sure you dont have have this problem again i would definetly buy the new design gasket kit.

you have a blown head gasket or cracked head