L200 overheating changed the thermostat no luck blowing cold air in cab over heats quicker when rev

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This is more than a heater or radiator core problem.
Let's assume that the radiator is full of coolant and is not blocked or the vanes badly corrodes. The thermostat has been changed, and still the engine overheats quickly.

Check for bubbles in the coolant when the engine is reved.
Is there any gray sludge around the radiator cap?
Is there white smoke from the exhaust?
Look at the oil. Is it milky or black?
Drop dipstick oil on to a hot exhaust manifold. Does it bubble or just smoke?

Any or all of the above suggest a blown head gasket. This is more than a heater or radiator core problem. Let's assume that the radiator is full of coolant and is not blocked or the vanes badly corrodes. The thermostat has been changed, and still the engine overheats quickly. Check for bubbles in the coolant when the engine is reved. Is there any gray sludge around the radiator cap? Is there white smoke from the exhaust? Look at the oil. Is it milky or black? Drop dipstick oil on to a hot exhaust manifold. Does it bubble or just smoke? Any or all of the above suggest a blown head gasket.