Hey guys! first post on this site but i frequent on another f150 forum and i always tend to read many posts from this site when i am googling on my phone and what not! very helpful! so i just bought a 98 f150 with the 5.4 4x4. so i will be driving for about 10 to 15 minutes and my coolant gauge will shoot way up to high and then the coolant light will turn on along with my check engine light with a p1299 (cylinder head temp sensor). as a side note do the 98s have the cht sensor because i have read that there was year where they cut off or something and didnt use them in some years but used them in others so i need to get that cleared up. Back to the problem, sometimes it will shoot up, and then fall back to normal operating temp. sometimes it will put the truck in limp mode running on four cylinders. also i would like to add that my upper radiator hose is getting hot like the thermostat is opening up to cool it off but the lower hose is not getting hot at all. or at least not nearly as hot as the upper hose. i bought it with a new radiator, i have replaced the two coolant sensors on the intake manifold and the thermostat as well. the main thing that makes me wonder is the truck runs strong until the computer is told to go into limp mode which is what i don't understand? there are also no leaks or anything or any coolant mixed with the oil and vice versa. i have also burped the coolant system to try and get the air bubbles, if any, out but i may not have done it correctly either. i have also been told it could be my water pump and i am starting think it could be something in my lower radiator hose as well? Any and all suggestions would be helpful. Sorry for the long first post just trying to give yall as much information as i had! Thanks for reading!