With reference to an earlier question in which I did not identify the make and model of car, the blinking D is not intermittent. It is constant. When I lifted the hood of the car to check the transmission fluid level, a small critter (rodent, too big for a mouse) fled from the engine. My neighbor and I noticed several wires chewed through and believe this to be the reason for the problem. I slowly drove the car to the dealer for a diagnostic check. As I drove the car revved high so I kept the speed down. Occasionally the transmission would jump to the next gear and it was a noticeable jump. It was a distance of about ten miles and I kept the speed to 35 miles per hour.
Am I right about the cause of the blinking D?

Most definitely.