I would suggest before old man winter takes a toll on you and your frozen,power flush the engine and radiator,just draining the radiator wont remove the contaminates ,you can buy products at the store,or take to like jiffy lube or something like that.to also do the job.
also buy the proper T-stat ,and check make sure your water pump is ok,cause been driving chevy's forever,or there is a concept buy a repair manual and read it,and be as smart as me,what does the radiator look like,if kinda gummed up that will also make you not heat up,if you flush that should do the cheap trick,if not,you always could buy a heating and plug it in.