Aaron, milky stuff AND not turning over sounds like hydrolock to me. If you try hard enough, you can bend a connecting rod REALLY BAD this way!
You need to remove ALL the spark plugs and THEN try to turn the engine over. BEFORE you even worry about a compression test. Use a remote starter switch, or hve someone else use the ignition while you observe under the hood. DO NOT STAND ON THE PASSENGER SIDE OF THE TRUCK. If the block has taken on water, it will shoot fast and far out of the side. Then you will know which cylinder are affected.
If the truck was this way when you got it, I wouldn't take a chance on the rods without dropping the oil pan and inspecting them too.