On a 2207 model, it could be the warp drive...
Seriously, though. No AFM on my 4.8. Not the issue. As stated, perhaps a thermostat issue. One other item to check is whether the fans are turning on properly as well. These models use a multispeed fan setup.
Two last things to consider are water pump and coolant. Proper coolant mix? Correct water pump flow?
Good luck! I know that these types of issues can be frustrating.