I have a 98 chevy K1500, 5.0 with 245,000. I have replaced head gaskets twice. Last set had heads looked at by machine shop said ok. using felpro heavy duty gaskets.replaced head bolts,water pump twice,fan clutch,radiator,4 thermistats from acdelco. all hoses.made sure was not vapor locked, system has no air. oh ya replaced radiator cap. thermistat is opening, upper hose is hot bottum hole is look warm. if thermistat is in the truck starts over heating if stat is out truck tuns 110 degrees. also gauges are accurate shot every thing with infered thermistat. if anyone can help please put your input...took truck to dealer and two different shops and they want to do everything i have done..