So, I had a heat problem with mine mentioned earlier in this post. Changed heater core, thermostat, hoses, coolant, checked door actuators, blend door, all checked out and still heat was not that great. I did an LS swap with a new engine from my old 305 since the post and the heating did get a bit better but still not that kind of heat where I recall 20+ years ago when I first got my truck, that it would almost force me to run out of the cab for dear life. So, I started to think backwards on what I did since the heat got worse, and I recall that I had changed to a bigger rad. This is when all my issues started. This truck had a much smaller rad before and I even removed the block plates that were from factory in front of the rad there to give this truck more cool air. Well, it seems that there has to be a balance with any vehicle so altering the ride size may give better cooling but may affect the heat in those cold winter months. I put the block off plates back and I did notice a big difference, I guess this would be like putting those winter grill bras on the grills that some in northern climates do. I then changed to a smaller rad and darn heat is back where it was like I remember it. So, just wanted to mention this as a potential solution especially if you upgraded the rad size or maybe the previous owner did at some point. With the new LS L33 all aluminum block and heads, this truck now warms up at least 5 times faster than it used to with the ole iron block 305.