Definitely need to do the 6.0 transmission cooler modification. Get yourself a transmission temperature gauge as well. The Viton front seal is a better option - it doesn't get soft when hot.
Here's a write-up on the cooler upgrade - View attachment 6.0 Transmission Cooler Write up.pdf
Here's a write-up on the cooler upgrade - View attachment 6.0 Transmission Cooler Write up.pdf