As a driver of a gasoline tankersometimes you would by accident cross drop product, so long as gallons in tanks came out as amount billed all was good.Some dealers would ask you to cross drop and slip you some green. some would also pump regular into premim tanks at night. also some woild change fill markings on tanks. So driver would not get blamed, one station in ny the tanks were marked different every time you went there !!!! I would nerver buy premium unless it was only thing available. delivered for over 25 years I have seen it ALL !!!!
Man, I don't know who you worked for or what stations you delivered to, but if we cross dropped (even regular vs super, let alone crossed gas and diesel) we were IMMEDIATELY fired! No messing around. Plus our pumps and/or store would be shut down. Huge liability.
The other issue is the state randomly would test all tanks to see what was in them, plus octane, plus to be sure you got a gallon. Again, huge liability.
Lastly, I've run regular in my expy for years, along with mid grade and premium on and off. NEVER a code. I'd think something else is wrong here, not octane. The computer will adjust for octane. I've even run 85/86 because that was all that was available on a trip once at a station. No codes. If you got diesel instead of gas, odds are it would shut down or blow up depending how much diesel was mixed in.