2005 Pontiac Grand Am overheating

My car is overheating. I replaced the thermostat first and bleed system filling tank it stop overheating for one day then it started again. Found a leak in the water pipe that goes across the front of eng all the way to a line by fire wall. Still overheating. Replaced water pump ran for a day or so and started the same problem. Check the small tubes from water re savor they were packed full of gunk no water going thru. I replaced them and put a new radiator. I thought problem was solved but it ran for a day and the problem changed a little. Now the heater keeps cutting off just cold air then the temp would go up and heater would work and temp would go down. So I replaced the thermostat again. This time I drove for 95 miles and no trouble. Thought it was solved but I drove it tonight and no heat so I stopped and check the coolant and bleed the system again. No luck I had to baby it home because nit keep overheating. It took me 1 and a half hrs to get it home. Put another gal of antifreeze in half way home when I checked it at home it was a gal low. By the way the old radiator was clogged bad with crud. I broke open the tank it had chunk's of crud in it. My question is where do I go from here. I don't think its a head gasket because the system holds pressure.
Thanks
William Rodriguez