The number one reason why people complain about their heater not putting out enough heat isn't the thermostat, it is actually bad coolant.
Most people assume as long as the coolant is green, that it's still good. This however is not the case. You should have the cooling system flushed out completely every 30,000 miles. What happens is the heat holding capacity of the liquid actually diminishes over time.
While you're doing this you can also change the T-stat. It's usually located on the engine side of the upper radiator hose. Make sure you also change the gasket and clean off all the sealing surfaces before putting it all back together.
As for the reversed heater hoses, this *could* be part of the problem, however once the engine reaches operating temperature, it shouldn't make that much difference.
Good luck!
Ben
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