Use the Mercon V, period.
I did the JMod to the valve body and added a transmission cooler. In all, it took 12.5 quarts of Mercon V. I had a bit of shudder before the Mercon V and JMod, but none since. I've done everything but mountain driving and drag racing with the transmission and no problems. That was 11,000 miles ago. This is not an ancedote, just fact.
The Parts Bin Special is DEAD! It is being parted out.