my dealer just charged me $595 to change the thermostat on my 2001 Tahoe LS (5.3) - they said the thermostat is connected to the water pump and cannot be separated so the water pump has to be replaced in order to change the thermostat - they said the water pump and thermostat costs $325 and the rest is labor - does this sound right? looking up online i find pumps for $100 - am i being ripped off? i hope someone can help ....