I've read the issues with the other dodge truck owners. My issues are similar. I replaced the thermostat, water pump, flushed the system and even ran radiator cleaner for 6 driving hrs. My truck runs fine on a mild temp. Day(70's-80's) but when the weather reaches higher then that my truck temp Gage reads about 1/4 over the middle temp line. Then the Gage proceeds to decline as I continue to drive at lower speeds. Or so it seems. It never seems to overheat, but it does seem as if it's running hotter then it should. My temp. Has run at a substantial improvement since I replaced all those things, but I'm not sure if I should be concerned with what's happening. Also I read about peoples heater blowing warm air. Mine does that as well. Just wondering if anyone could shed some light on the situation. Any advice will be appreciated. Oh. How do you flush a heater core? Thanks.

Build-up from minerals in the coolant/water mixture may have over time congested some of the tubes in your radiator, thereby reducing it's efficiency.
Using a flush additive only cleans the tubes that are still open to flow. The same may be happening to your heater core, only to a smaller extent.
The best way I know to see if this is your problem would be to use an infra-red temperature probe The kind you point at an object and read it's temperature (I like the Raytek Mini: Amazon.com: raytek mini). They're under $50.00
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Have the cooling system up to temp: both upper and lower radiator hoses are hot.
Scan with the infra-red device along each tube and tank on your radiator, looking for cooler spots, usually towards the bottom of the radiator.

Replace the radiator or have it rodded. Phosphate scale build-up has likely greatly reduced its ability to transfer heat. Afterwards, only use a 50/50 mixture of the recommended antifreeze and distilled water. Change coolant every 2 to 3 years.

This link should help:

https://www.askmehelpdesk.com/cars-t...tml#post235973