I've Got This Engine In My 250 Superduty, Just Went Over 100,000 And Am Religious About Changing The Oil. Should I Be Thinking At This Stage About Using A Full Synthetic?

you could but it would be better to use regular, because full synthetic is better if u use it when the truck was brand new. after 100,000 it would be pointless. it is really up to u though. if you do use full syntetic i think u have to gradually introduce it into the engine.