Low engine temperature

I have a 1992 ford ranger with a 2.3 4cyl. The temp guage will no go into the normal range and it blows only warm heat not hot. I have replaced the thermostat twice, heater core, water pump, hoses, and head gasket. After replacing the water pump temp did run in normal range for a couple of days but then dropped down again. I've taken to a shop to have the radiator flushed and was told flow was good. They played with it for a week even tried removing the fan and blocking the radiator. It still ran cool. Took it to a second shop and was told head gasket. After changing head gasket it seems to run cooler.