to all you guys struggling with the p1299 code and your truck is not overheating but it keeps going into limp mode check your wiring harness when it runs up next to the evaporator and plugs into the junction block with all the other wires mine rubbed thru and got one out of the two wires for my (cht)cylinder head temp sensor causing it to ground out and think it was over heating hope this helps

 

I racked my brain with this problem for 3 months I replaced the radiator water pump thermostat and the cylinder head temp sensor no results I also checked the harness that runs to the sensor itself I never thought to look that far away from the sensor itself