Ill put my 2 cents in
my 96 xj was putting out Warm air but not like it was when she was new so i did what most have done and backed flushed the heater core except i filled my heater core with CLR and let it sit for about 30 minutes, then i just flushed it out with a water hose ( make sure you put the hose in an empty jug to get the used CLR) once it was running clear with the water i put all back together and now i can roast marshmallows from the heat
