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Hello and thank you for your question,When the check engine light come on have you scanned it to see what fault code is setting?
I'm not finding the code P1089 to be a valid code but I would agree with you, this does sound like a problem with the temp sending unit and the 5.0 uses a CHT (cylinder head temp sensor) in its place. The CHT is located on the back side of the RH cylinder head and unfortunately to access it you will need to remove the intake. Before you go that far, can you recheck the fault code and let me know and I will advise from there.