IF it's running ok with no codes, I'd place my bets on incorrect engine coolant, i.e., Dexcool or plain water. I had a Charger with the 5.7, and discovered muddy coolant while replacing the water pump. The previous owner had used Dexcool. I had to have it flushed 3 times. It did eat another water pump after the fact, but that's because they're junk to begin with.
The fix, if it is bad or incorrect coolant, would be less expensive, depending on how many times the engine would need to be flushed, who's doing the work, and whether or not they use the correct OAT coolant, with at least a 50/50 mix (I use 60/40).
You can also expect to lose your water pump and probably heater core(s) in the near future.
If the car runs like crap, it's conceivable you may have a head sealing issue, but it would likely have been caused by the incorrect coolant and the corrosion/plugged up coolant ports resulting thereof. I've had more than a few head gaskets go on me, and not one of them had muddy coolant. Muddy coolant is most common in vehicles with aluminum heads and/or the block.
Good Basic Tips
Whether it's the 3.6 or any of the V8 models:
1) Always used the correct coolant for the model year (owners manual)
2) Never used just water
3) Always run the correct 203° thermostat
4) Check the coolant level at least once per week, while checking the oil and brake fluid levels