Sambo,
As you know my set up is similar to yours, having a cam/tune does
Nothing to alleviate the busyness of the final drive.
I changed my diff from 3.9 to 3.5 as I thought the 3.9 was too busy,
I should have left it alone ( people have been telling that for ever
) the 6
Speed is useless on the highway and the 3.9 would have been better on the
track.
The actual redline is closer to 7000rpm so take that into consideration also.
Stiffy