I've used the T6 5W-40 on my 3.0 and the only thing I noticed was a 2MPG decrease in mileage when I changed. I posted my results on here and everyone thought I was nuts, but it was reproducible every time. When I switched back to 5W30, my mileage came back. When I switched to T6 it dropped by exactly 2MPG.
What climate do you live in? It may be a bit thick for below freezing weather.