GMC 2500 1992 code 15 coolant temp sensor ...Put a new one in still the same..

Hello, sounds like perhaps the engine is not getting to proper operating temperature? Or the coolant temperature sensor is defaulting "low". I don't think that's a cause of anything, rather the effect of what is happening with your running concern. Need more information about "starting or running right" - what is the truck doing, and what testing has been performed? www.repairpal.com/repair-shops