GM-GMC: 97 Chevy truck, chevy silverado, coolant level

Question
I'm having a problem maintaing the proper coolant level in my truck. It is a 1997 Chevy Silverado with a 5.7 liter engine. My local mechanic has did a pressure test and couldn't find a leak. There is no water in the oil. A couple of people have told me about a gasket toward the  back of the engine that has become a common problem with this particular make and model. Can you tell me anything about this?  Thanks for your help.  

                                           Jim

Answer
I can run a recall, special policy, and Technical service bulletin check through my system but if I find any you would have to purchase it to get a copy. I run a service for this sort of thing. All I need is the vin to run the check if I find anything I will let you know and you can decide what to do.