Hopefully your issue has resolved itself by now, if not I have a few suggestions & a little knowledge to pass on (can't take it with me so might as well give it away). Now you have addressed all the common issues from heater core to coolant in the exhaust. Please only use those fix a leaks as a hail Marry they usually destroy your engine by blocking all of your small water jackets or radiator. Being an R/T you have a timing belt, I assume it was replaced at 100k miles (160934.4km) was the water pump replaced at the same time? Water pumps have a weep hole on them & your coolant can be coming from that hole onto the motor, evaporating on the hot engine, leaving no liquid mess but a nice white & green (depending on the color of the antifreeze) trail. I don't know if you turn your own wrenches but I never trust anyone (sad I know) also make sure your serpentine belt is routed the correct way especially on the water pump. If it is not spinning the correct position it can't do it's job. Last but not least if you've over heated in the past or have never addressed it, replace the temp. sensor. They are relatively cheap & once it overheats, or hasn't been changed out, it's time for a new one. That way you can see if your temp is running higher than norm. Good Luck.