Yes, I have a diffuser made. I have no idea if there are decent gains as yet due to the extreme cold and blowing snow. The car has a number of underbody treatments that smooth the airflow, but not smooth enough to introduce a good smooth stream of air to the diffuser. So the gains from the diffuser are not fully realized until I get a full smooth pan made. That will be in spring sometime. Also, my diffuser is at a 12 degree angle. That is too steep. So, I need to make some minor alterations once the weather permits. I can tell you that the waterlines left on the diffuser tell me the airflow is staying attached and relatively smooth. So, that is good.
The car has over 47,000 miles on it so far and I still love it. Oh, of that 47,000 miles, 27,000 have been EV and this car is not a plug in.
Gotta love it.
Oh, it was 2 degrees today and I still averaged 43mpg........
Matt