98 Ram 2WD 5.9

I think I am having the ol "heater works okay till I turn the fan on high" woes. Do I get hot/warm air out of the floor duct? Yes. But when I turn the fan on high it "feels" cooler. I tried putting in Prestone flushing solution and then backflushing my system. Didn't seem to help. And my core gurgles now. NO, I didn't jack up my the front side of my truck when filling with coolant, because the radiator cap is higher than anything in coolant system when the truck is sitting on level ground, isn't it? I measured the temperature of the air and it is abiut 120*. Anybody know what it is supposed to be?

As a last ditch effort before I do the heater core exchange torture session, I'm thinking about filling the core with CLR by disconnecting the heater hoses at my backflush T fitting and at the water pump, blowing out all the coolant and then filling with CLR. After it sits a while then truly backflushing the core by attaching a garden hose to the water pump side hose and forcing water back thru the core and catching it all in a bucket just to see what comes out. Thoughts

 

um, actually when level, the heater core sits higher

 

Well, all righty then, I'm off to jack up the front of my truck. Or find a hill. Thanks