E is the 8th digit.
Information is appreciated but mainly I wanted to consult with someone to determine if the tire size issue would be a likely easy fix by replacing the tires. I'm planning on a big family trip tomorrow and might need to use the other (smaller) vehicle.
I opted out so another expert could try to give you more detailed information about your problem. The size of the tires " new versus the old" Will not be enough to cause the o/d light to flash. For the light to flash there would have to be a problem within the transmission. If it where my truck I would not take it on a long trip till I had taken it to a transmission shop to have it checked out. If the tire size had been the cause of the o/d light flashing you would also have an abs light on.