1994 Suburban, 1500.

It started with a radiator leak. I replaced the radiator. Then the heater core began leaking. Replaced it. The new one started leaking. Replaced it. Now the new radiator is leaking! I've replaced the thermostat, system has the proper mix of coolant/water, and I'm now at a loss. What the heck is going on with this thing? The engine is not overheating.

Radiator cap maybe? Or cheap imported parts, (radiator, and heater cores)? Or something else? Any ideas at all?

I would go ahead and replace the radiator cap just in case the system isn't maintaining proper pressure. Aside from that, the only other component of the coolant system left to look into/replace would be the water pump. Maybe a coolant blockage somewhere in the engine block? Dunno...it's hard to say.

I went through 4 heatercores in my mustang due to shoddy japanese workmanship. I bought a new one and took it to a radiator guy who soldered the hell out of the connections and I've been fine since :)

I'm going to replace the radiator cap, (though I don't believe there's anything wrong with it). I'll recrimp the leaking area on the radiator, (it's at the junction of the side tank, which is plastic, and the aluminum body of the radiator). The water pump seems fine, plenty of coolant flow, so I don't think that's the problem either.