Hello Steve,
I am a newcomer on this forum as well, and I did not sleep at a Holiday Inn last night.
Synthetic oil will not hurt your truck because chemically it's not so different from dyno oil apart from some impurities in dyno. Dyno oil has carbon chains of various sizes, because they can't filter it as much as they would like to. Synthetic oil is made chemically from scratch, and they can make carbon chains exactly the size they want for better lubrication and cooling. Carbon chains are like balls of different sizes, say golf balls and basket balls. If you were body surfing on a carpet made with balls of different sizes, it would not be as comfortable as surfing on a carpet composed entirely of golf balls. Same thing for lubrication.
I don't know Shaefer but I use Shell Rotella T6 full synth in everything I own that needs motor oil, including a 35 year old Honda motorcycle that I love dearly.
I wasn't aware that some premium fuels had ethanol in them, but I always use premium and I'll keep an eye on what's in it from now on. Using premium when the owner's manual says regular is useless, using regular when the manual says premium is asking for trouble.
You do not mention what code you got exactly, so it's kind of hard to comment on that.
Georges
Georges Payne
2003 Disco II SE-7