2004 Silverado Internal Coolant Leak

I got a 2004 Silverado 1500 5.3L with 79,000miles. Several months ago it started smoking on start up. I changed the oil and noticed it was sludgy. I also noticed that the coolant level was low. I thought it was obvious that it had an internal coolant leak. I took it to the local Goodyear place and had them take a look at it, and they said it needed a new water pump, theromostat, radiator, and upper and lower hoses. Now, all I can assume is that they did the compression checks and found nothing out of the ordinary. I was thinking head gasket or cracked head, Can coolant mix with engine oil through a faulty water pump?