1995 Toyota Camry Head gasket blows repeatedly after overha

I'm looking for an objective opinion. My Camry has been faithful but the engine (a 5 SFE) was developing a sludge problem. I went ahead and had the engine overhauled and installed by a reputable engine shop. Six thousand miles later the head gasket blew and the block was damaged. The car went back to the shop for a second rebuild and three thousand miles later the head gasket blew again. Bear in mind that all hoses, belts and the radiator were replaced the first time around.

We are now looking at a third rebuild with the shop standing behind their work; however, while they express their intent to scrutinize the rebuild, they appear somewhat baffled as to the cause of these failures and surmise there is an overheating problem outside the engine. They rebuild/ship over 100 engines a month and don't believe / see how they could be missing something in the rebuild that might cause this repeatative behavior.

I intend to install a secondary water temp gauge; however, while I 'd like to keep it I no longer trust the car and unless I can assure myself it won't fail again I feel I need to sell it immediately. ( I don't like the idea of passing along a potential major problem.) Can you suggest some ideas, perhaps beyond the engine, that might help isolate this recurring problem? Also, the exhaust system and catalytic converters were checked prior to the second rebuild.