heating problem 1997 dodge ramm 1500

can some one tell me why my dodge ram 1500 with a 318 will not put out heat it has a new radiator,1 freeze plug replaced,heater core not stoped up,when its cool outside,say below 70 the truck runs about 130 to 150 degrees,it also has a new themistat,192 degrees the truck can run for an hour in the morning and never put out heat,in the summer the truck runs normal temp about 200,this has been going on for 4 years i am ready to install a wood stove,if you can help please send me an email ( everhart4@yahoo.com) thank you so much
Author: thisram