My 1998 S-10 blazer 4wd keeps over heating. I have replaced the thermostat, had the system flushed, (which they said there was no blockage cuz it was flowing good) replaced the clutch and fan blades, cleaned the condenser and radiator to ensure proper air flow, also replaced temp sensor sending unit. The water pump is circulating. And thermostat is opening and closing but I keep overheating to the point steam is coming out the overflow tube. I'm not losing fluid and it's not mixing into the oil or tranny. What am I missing?