Don't switch to 10w40. You should be using 5w30 or 5w20. Don't bother with the additives either. If your engine is getting so worn out that it would require higher viscosity oil, then higher viscosity oil wouldn't help anything anyway. Running that higher weight oil will just accelerate engine wear, especially at startup, which is really when most engines see the most wear anyway. If clearances between moving parts were already that large that you would need a 40 weight oil, then you would need to be thinking of an engine rebuild. My engine is full of motorcraft semi-synthetic 5w20 by the way, and it is higher mileage than yours. Between Minnesota, North and South Dakota, where most of my driving is, my Explorer will see temperatures between -45 and 110.
The correct oil for your engine, according to ford, is 5w20. Original spec was 5w30, the TSB changed that to 5w20.